Mixing Nimhs in multi-battery usage

[jt4703]

I know the rule with alkaline is to not mix brands or different levels of use, however does the same rule apply to Nihms? I have some energyON LSD batteries I've had for a while and I bought some new eneloops. Both batteries are 2000mah and LSD. If I use my Maha 9000 charger to match capacities, can I safely use the two brands together? Could I mix nihms of different original capacities that have the same current capacity? What about using HSD and LSD together that have the same current capacity?

 

[jhellwig]

No.


Only mix batteries from the same batch and with the same amount of use and abuse on them.

 

[Turbo Guy]

Rules are made to be broken. While it is advised to use NiMH cells in matched sets I have very often over the years mixed similiar cells. I have had a cell or two in a 8 cell battery to go south and have replaced it with a new or atleast newer cell. As long as the application is not a very high drain one and you do not overdischarge the weakest/lowest capacity cell it will be fine. Since you are using C-9000 to grade(match) the cells I would not worry about it. I would not mix LSD with others however unless they are all fresh off of charge and will be used right away.

I suspect that most just have a stach of NiMH cells that were never matched and kept in sets and that they are just charged and used randomly. Not the best thing to do but it works for them.

 

[SilverFox]

Hello Jt,

When breaking the rules I feel it is important to understand why the rules were made in the first place.

If you mix used and new alkaline cells, they usually will leak. If you mix used and new Lithium or Lithium Ion cells, they can rapidly vent, sometimes with flame. It is best to abide by the rules when using these chemistries.

That brings us to NiMh and NiCd cells. If you mix used and new NiMh cells, you run the risk of damaging a cell through voltage reversal during a deep discharge. If you were charging the cells as a battery pack, you could also destroy a cell during charging, but that is not a concern in this case.

It is always best to match cells, but as you can see, with NiMh cells there is only a little downside in breaking that rule. As long as you can live with the "loss of performance" and adjust your expectations of cycle life, have at it.

Tom

 

[TakeTheActive]

...I know the rule with alkaline is to not mix brands or different levels of use, howeI have some energyON LSD batteries I've had for a while and I bought some new eneloops. Both batteries are 2000mah and LSD. If I use my Maha 9000 charger to match capacities, can I safely use the two brands together? Could I mix nihms of different original capacities that have the same current capacity?

The C9000 is measuring capacity, like a bathroom scale measures weight. It's not reading the labels or determining the age. If two NiMH cells are both reading ~1800mAh, as far as the C9000 (and MOST devices you could use the cells in) is concerned, they're matched - just like the bathroom scale cannot tell the difference between 100lbs of human being vs 100lbs of potatoes.

...What about using HSD and LSD together that have the same current capacity?

Now you've added time and "Self-Discharge" into the picture. While you may have two five gallon pails, HSD and LSD, full of water, the HSD pail has more holes in it. If you use the stored energy in both cells BEFORE the HSD 'leaks out', it should make no practical difference. But, for example, if you wait a week, or a month, and then attempt to use the energy, the cells will no longer be matched since the HSD will have 'leaked out' more energy than the LSD.

That said, there can also be many other variables involved - internal resistance, maximum voltage available under load, maximum current available - but even identical cells (same manufacturer, same batch, same age, same original capacity) can drift apart. Only you, not the C9000, can determine how suitable they are as 'matched cells'. Try them once and see how they perform.

CLICK on my Sig Line LINK for loads of interesting reading that I've gathered from the CPF 'Batteries Included' Archives.

 

[Russel]

The C9000 is measuring capacity, like a bathroom scale measures weight. It's not reading the labels or determining the age. If two NiMH cells are both reading ~1800mAh, as far as the C9000 (and MOST devices you could use the cells in) is concerned, they're matched - just like the bathroom scale cannot tell the difference between 100lbs of human being vs 100lbs of potatoes.....

Once you match a set of cells by measuring their capacity with the C9000 wouldn't the next step be to measure the energy required to recharge each cell after being discharged as a set? For example, match two cells by measured capacity then place them in a flashlight (2 AA cells in series), discharge approximately 2/3 of the cells capacity, then compare the amount of energy required to recharge each cell. Would the recharged capacity be close or the same if both cells had the same capacity and different internal resistance?

 

[jt4703]

Thanks for the advice. I'll probably end up mixing my LSD AA since I have an odd number but I'll be sure to use those with similar capacities. I'm not too worried about run time since my commute is fairly short and I've got spares on the bike.

 

[TakeTheActive]

Once you match a set of cells by measuring their capacity with the C9000 wouldn't the next step be to measure the energy required to recharge each cell after being discharged as a set? For example, match two cells by measured capacity then place them in a flashlight (2 AA cells in series), discharge approximately 2/3 of the cells capacity, then compare the amount of energy required to recharge each cell...

jt4703's non-text URL in: Mixing NiMh brands got me to read this thread again and I see no one ever replied (I wasn't feeling too hot health-wise the first time I read it and I meant to get back to it... 😱 ).

The impression I got the first time I read this was "This is a 'Trick' question, right?" 😕 and, almost a week later, I feel the same way. From everything I've learned, as a hobbyist - not an engineer, CURRENT in a SERIES circuit is constant (and VOLTAGE in a PARALLEL circuit is constant). We make use of this 'Constant CURRENT Rule' when we use a resistor to measure the INTERNAL RESISTANCE of a cell.

If I discharged a pair of LSD NiMH cells in my C9000 @ 100mA and it came up with ~1900mAh, then if I put that pair into a device that draws 100mA, ~19 hours later they should be empty. When I recharge them, both at the same rate / time / temperature, they should terminate at approximately the same time (i.e. take in the same amount of charge).

Why would you think otherwise? :thinking:

...Would the recharged capacity be close or the same if both cells had the same capacity and different internal resistance?

I'd say NO! If they had different internal resistance, they would also have different measured CAPACITY.

I've been going through my *CRAP* cell today and discovered something applicable:

NiMh Rayovac         AA 1600ma  1: 04/10/09 - 1.55VDC (Impedance Check C9000) ENV-Y
NiMh Rayovac         AA 1600ma  1: 02/19/09 - 1299mAh (Refresh3   BC-900  200) ENV-Y
NiMh Rayovac         AA 1600ma  1: 02/xx/09 - 1298mAh (Refresh2   BC-900  200) ENV-Y
NiMh Rayovac         AA 1600ma  1: 02/xx/09 - 1218mAh (Refresh1   BC-900  200) ENV-Y
NiMh Rayovac         AA 1600ma  1: 02/15/09 -  ---mAh (Charge RadioShk140/13) ENV-Y

NiMh Rayovac         AA 1600ma  2: 04/10/09 - 1.55VDC (Impedance Check C9000) ENV-Y
NiMh Rayovac         AA 1600ma  2: 02/19/09 - 1228mAh (Refresh2   BC-900  200) ENV-Y
NiMh Rayovac         AA 1600ma  2: 02/xx/09 - 1093mAh (Refresh1   BC-900  200) ENV-Y
NiMh Rayovac         AA 1600ma  2: 02/15/09 -  ---mAh (Charge RadioShk140/13) ENV-Y

NiMh Rayovac         AA 1600ma  3: 04/10/09 - 1.52VDC (Impedance Check C9000) ENV-Y
NiMh Rayovac         AA 1600ma  3: 02/11/09 - 1209mAh (Break-In  C-9000) ENV-Y
NiMh Rayovac         AA 1600ma  3: 02/09/09 - 1286mAh (Discharge C-9000  100) ENV-Y
NiMh Rayovac         AA 1600ma  3: 02/08/09 -  170mAh (Charge    C-9000  800) ENV-Y
NiMh Rayovac         AA 1600ma  3: 01/19/09 - 1378mAh (Refresh   BC-900  500) ENV-Y

NiMh Rayovac         AA 1600ma  4: 04/10/09 - 1.52VDC (Impedance Check C9000) ENV-Y
NiMh Rayovac         AA 1600ma  4: 02/11/09 - 1201mAh (Break-In  C-9000     ) ENV-Y
NiMh Rayovac         AA 1600ma  4: 02/09/09 - 1268mAh (Discharge C-9000  100) ENV-Y
NiMh Rayovac         AA 1600ma  4: 02/08/09 -  191mAh (Charge    C-9000  800) ENV-Y
NiMh Rayovac         AA 1600ma  4: 01/19/09 - 1368mAh (Refresh   BC-900  500) ENV-Y


NiMh Rayovac         AA 1600ma  7: 04/10/09 - 1.50VDC (Impedance Check C9000) ANL
NiMh Rayovac         AA 1600ma  7: 02/14/09 - 1236mAh (Break-In  C-9000) ANL
NiMh Rayovac         AA 1600ma  7: 02/12/09 - 1241mAh (Discharge C-9000  100) ANL
NiMh Rayovac         AA 1600ma  7: 02/11/09 -  300mAh (Charge    C-9000  800) ANL
NiMh Rayovac         AA 1600ma  7: 01/21/09 - 1280mAh (Refresh   BC-900  700) ANL
NiMh Rayovac         AA 1600ma  7: 01/20/09 - ----mAh (Charge    BC-900 1500) ANL
NiMh Rayovac         AA 1600ma  7: 01/20/09 - ----mAh (Charge    BC-900 1800) ANL

NiMh Rayovac         AA 1600ma  8: 04/10/09 - 1.53VDC (Impedance Check C9000) ANL
NiMh Rayovac         AA 1600ma  8: 02/14/09 - 1225mAh (Break-In  C-9000) ANL
NiMh Rayovac         AA 1600ma  8: 02/12/09 - 1228mAh (Discharge C-9000  100) ANL
NiMh Rayovac         AA 1600ma  8: 02/11/09 -  176mAh (Charge    C-9000  800) ANL
NiMh Rayovac         AA 1600ma  8: 01/22/09 - 1220mAh (Refresh   BC-900  700) ANL

NiMh Rayovac         AA 1600ma  4: 04/10/09 - 1.69VDC (Impedance Check C9000) ANL
NiMh Rayovac         AA 1600ma  4: 02/14/09 - 1188mAh (Break-In  C-9000) ANL
NiMh Rayovac         AA 1600ma  4: 02/12/09 - 1238mAh (Discharge C-9000  100) ANL
NiMh Rayovac         AA 1600ma  4: 02/11/09 -  191mAh (Charge    C-9000  800) ANL
NiMh Rayovac         AA 1600ma  4: 01/24/09 - 1319mAh (Refresh   BC-900  700) ANL

NiMh Rayovac         AA 1600ma  2: 04/10/09 - 1.93VDC (Impedance Check C9000) ANL
NiMh Rayovac         AA 1600ma  2: 02/11/09 - 1147mAh (Refresh   BC-900  200) ANL
NiMh Rayovac         AA 1600ma  2: 01/20/09 -  714mAh (Refresh   BC-900 1000) ANL


NiMh Rayovac         AA 1600ma  3: 04/10/09 - 1.57VDC (Impedance Check C9000) ONN-Y
NiMh Rayovac         AA 1600ma  3: 02/11/09 - 1184mAh (Break-In  C-9000     ) ONN-Y
NiMh Rayovac         AA 1600ma  3: 02/09/09 - 1086mAh (Discharge C-9000  100) ONN-Y
NiMh Rayovac         AA 1600ma  3: 02/08/09 -  917mAh (Charge    C-9000  800) ONN-Y
NiMh Rayovac         AA 1600ma  3: 01/21/09 - 1354mAh (Refresh   BC-900  700) ONN-Y

NiMh Rayovac         AA 1600ma  1: 04/10/09 - 1.68VDC (Impedance Check C9000) MTB
NiMh Rayovac         AA 1600ma  1: 02/11/09 - 1174mAh (Break-In  C-9000     ) MTB
NiMh Rayovac         AA 1600ma  1: 02/09/09 - 1219mAh (Discharge C-9000  100) MTB
NiMh Rayovac         AA 1600ma  1: 02/08/09 -  185mAh (Charge    C-9000  800) MTB
NiMh Rayovac         AA 1600ma  1: 01/24/09 - 1365mAh (Refresh   BC-900  700) MTB

NiMh Rayovac         AA 1600ma  2: 04/xx/09 - ----mAh (Break-In  C-9000 1600) LNH-Y
NiMh Rayovac         AA 1600ma  2: 04/10/09 - ----mAh (Discharge C-9000  100) LNH-Y
NiMh Rayovac         AA 1600ma  2: 04/10/09 - 1.72VDC (Impedance Check C9000) LNH-Y
NiMh Rayovac         AA 1600ma  2: 02/15/09 - 1160mAh (Refresh2   BC-900  200) LNH-Y 
NiMh Rayovac         AA 1600ma  2: 02/xx/09 -  905mAh (Refresh1   BC-900  200) LNH-Y
NiMh Rayovac         AA 1600ma  2: 01/28/09 - 1214mAh (Refresh   BC-900  500) LNH-Y
NiMh Rayovac         AA 1600ma  2: 01/18/09 - 1216mAh (Refresh   BC-900 1000) LNH-Y

NiMh Rayovac         AA 1600ma  2: 04/10/09 - 1.84VDC (Impedance Check C9000) MTB
NiMh Rayovac         AA 1600ma  2: 02/14/09 - 1125mAh (Break-In  C-9000     ) MTB
NiMh Rayovac         AA 1600ma  2: 02/12/09 - 1108mAh (Discharge C-9000  100) MTB
NiMh Rayovac         AA 1600ma  2: 02/11/09 -  149mAh (Charge    C-9000  800) MTB
NiMh Rayovac         AA 1600ma  2: 01/28/09 - 1288mAh (Refresh   BC-900  500) MTB
NiMh Rayovac         AA 1600ma  2: 01/24/09 - 1198mAh (Refresh   BC-900  700) MTB

During the C9000 IMPEDANCE CHECK, the voltage momentarily displayed corresponds rather nicely to the measured CAPACITY (i.e. the LOWER the VOLTAGE, the HIGHER the CAPACITY; this is the FIRST time for the majority of the Rayovac 1600mAhs in the C9000 so we'll see how this 'theory' pans out. AGE also plays a part here since I don't expect to see +90% CAPACITY even on those (surprisingly LOW resistance) 1.5_VDC ~7+ year-old cells.).

[Another 'experiment' on my To-Do List is to create a chart comparing the voltage displayed during a C9000 IMPEDANCE CHECK with the measured INTERNAL RESISTANCE using a resistor and a DMM. My 'Round Tuit' seems to have rolled somewhere... :shrug: ]

Compare those numbers above to today's batch of !TRASHED! cells:

NiMh Rayovac     AA 1600ma  1: 04/10/09 - 'HIGH'  (Impedance Check C9000) ONV-Y !TRASH!
NiMh Rayovac     AA 1600ma  1: 04/10/09 - 2.11VDC (Impedance Check C9000) ONV-Y
NiMh Rayovac     AA 1600ma  1: 04/10/09 -  *WARM* (Charge    PS-3    500) ONN-Y
NiMh Rayovac     AA 1600ma  1: 04/10/09 - 'HIGH'  (Impedance Check C9000) ONN-Y ?TRASH?
NiMh Rayovac     AA 1600ma  1: 04/10/09 - 2.39VDC (Impedance Check C9000) ONN-Y
NiMh Rayovac     AA 1600ma  1: 02/18/09 - 1102mAh (Refresh2   BC-900  200) ONN-Y ?Recycle?
NiMh Rayovac     AA 1600ma  1: 02/xx/09 -  871mAh (Refresh1   BC-900  200) ONN-Y
NiMh Rayovac     AA 1600ma  1: 01/28/09 - 1171mAh (Refresh   BC-900  500) ONN-Y
NiMh Rayovac     AA 1600ma  1: 01/22/09 - 1088mAh (Refresh   BC-900  700) ONN-Y

NiMh Rayovac     AA 1600ma A2: 04/10/09 - 'HIGH'  (Impedance Check C9000) ONV-Y !TRASH!
NiMh Rayovac     AA 1600ma A2: 04/10/09 - 2.43VDC (Impedance Check C9000) ONV-Y
NiMh Rayovac     AA 1600ma A2: 04/10/09 -  *WARM* (Charge    PS-3    500) None
NiMh Rayovac     AA 1600ma A2: 04/10/09 - 'MODE'  (Impedance Check C9000) None ?TRASH?
NiMh Rayovac     AA 1600ma A2: 02/17/09 - 'HIGH'  (Break-In       C-9000) None ?Recycle?
NiMh Rayovac     AA 1600ma A2: 02/17/09 - 1191mAh (Refresh3   BC-900  200) None
NiMh Rayovac     AA 1600ma A2: 02/xx/09 - 1175mAh (Refresh2   BC-900  200) None
NiMh Rayovac     AA 1600ma A2: 02/xx/09 - 1158mAh (Refresh1   BC-900  200) None
NiMh Rayovac     AA 1600ma A2: 02/12/09 -  ---mAh (Charge RadioShk140/13) None
NiMh Rayovac     AA 1600ma A2: 02/12/09 -  ---mAh (Discharge Superman) None
NiMh Rayovac     AA 1600ma A2: 02/11/09 -    0mAh (Discharge C-9000  100) None
NiMh Rayovac     AA 1600ma A2: 02/11/09 - 'HIGH'  (Charge    C-9000  800) None
NiMh Rayovac     AA 1600ma A2: 01/20/09 - 1265mAh (Refresh   BC-900  700) None

NiMh Rayovac     AA 1600ma  1: 04/10/09 - 'HIGH'  (Impedance Check C9000) ONV-Y !TRASH!
NiMh Rayovac     AA 1600ma  1: 04/10/09 - 2.45VDC (Impedance Check C9000) ONV-Y
NiMh Rayovac     AA 1600ma  1: 04/10/09 -  *WARM* (Charge    PS-3    500) ONV-Y
NiMh Rayovac     AA 1600ma  1: 04/10/09 - 'MODE'  (Impedance Check C9000) ONV-Y ?TRASH?
NiMh Rayovac     AA 1600ma  1: 02/13/09 - 1085mAh (Refresh2   BC-900  200) ONV-Y ?Recycle?
NiMh Rayovac     AA 1600ma  1: 02/12/09 -  585mAh (Refresh1   BC-900  200) ONV-Y
NiMh Rayovac     AA 1600ma  1: 01/20/09 -  858mAh (Refresh   BC-900 1000) ONV-Y
NiMh Rayovac     AA 1600ma  1: 01/20/09 - ----mAh (Charge    BC-900 1500) ONV-Y 
NiMh Rayovac     AA 1600ma  1: 01/18/09 -  648mAh (Refresh   BC-900 1000) ONV-Y

NiMh Rayovac     AA 1600ma  3: 04/10/09 - 'HIGH'  (Impedance Check C9000) ONV-Y !TRASH!
NiMh Rayovac     AA 1600ma  3: 04/10/09 - 2.40VDC (Impedance Check C9000) ONV-Y
NiMh Rayovac     AA 1600ma  3: 04/10/09 -  *WARM* (Charge    PS-3    500) ONV-Y
NiMh Rayovac     AA 1600ma  3: 04/10/09 - 'MODE'  (Impedance Check C9000) ONV-Y ?TRASH?
NiMh Rayovac     AA 1600ma  3: 02/11/09 - 1065mAh (Refresh   BC-900  200) ONV-Y ?Recycle?
NiMh Rayovac     AA 1600ma  3: 02/07/09 -  661mAh (Refresh   BC-900  700) ONV-Y
NiMh Rayovac     AA 1600ma  3: 02/06/09 -  396mAh (Charge    BC-900 1000) ONV-Y

NOTE: This 'overly-wordy' single-line style of Charge Log is a carryover from my Excel spreadsheet where, since the majority of my NEW NiMH cells were Rayovac (1600mAh), I was tracking them by the BATCH IDs printed on them (instead of numbering them from 1-N). For my non-Rayovac cells, I've switched over to the 'Table' format that you'll see in my other posts.

 

[uk_caver]

When it comes to mixing NiMH cells, presumably a lot will depend on what they're being used to power.
If the target equipment is such that it stops working and stops drawing much current when the first-to-empty cell is discharged, then even with random mixing of cells of varying age and capacity, the downside might not be much worse than having the runtime determined by the worst cell.

Such equipment might include 3-cell LED lights without voltage-boosting circuitry, or (if they exist) other lights which had a deliberate cutoff circuitry built in to prevent overdischarge.

On the other hand, something which sucked every last drop of juice out of a battery pack as a whole could end up causing the least-good cell in a set to age very rapidly.
However, you could counter that by recharging your your cells pre-emptively, which in the case of a bike light, you might well be doing anyway, to reduce the chances of having to swap in a spare set in the middle of a journey.

If you have one cell that is discharged, and stick that in your light alongside others that are part-charged, does the light work as normal?

 

[Lynx_Arc]

it is possible to mix nimh cells of similar capacity and type (LSD vs non LSD). I think there are two issues involved in mixing cells, first the capacity and second the internal resistance. If these are nearly identical the chances of mixing them will be greatly improved but if these differ too much then you will get uneven discharging of cells and even cell reversal is very probable if discharged too much. You could do a test of sorts and run the mixed cells to perhaps 20% of the total runtime of the device and measure the voltage of all cells, then recharge them with an analyzer and check the used energy of each cell. If they voltages and energy used out of the cells (restored by the charger) is very close then you could proceed to perhaps a 50% usage test and so on.
I am guessing most likely if it is a low current device used to only 50% capacity you have a chance at mixing cells with no problems but at higher currents and a full discharge you stand great risks of cell damage when some cells discharge faster than others and are depleted completely, even reversal is very likely.

 

[uk_caver]

Does internal resistance matter, except maybe as a guide to how worn-out a cell is?

If, after a partial discharge from full, it then takes different amounts of charging to get each cell full again (or rather, it takes different amounts of charging until the charger thinks each cell is full), what does that actually say about each cell?

Does the partial or total charge-vs.-discharge efficiency of a given cell reveal much about its state of health?

 

[jt4703]

If you have one cell that is discharged, and stick that in your light alongside others that are part-charged, does the light work as normal?

I've yet to put a 'half dead' battery together with fresh ones, mostly because I want fresh batteries for my ride. When I need fresh cells in a light I change all the cells in it, not just one, and put the spent ones in a holder TBC over the weekend. I used to keep meticulous pairs since I charged all my cells on a maha 204F, so I neglected my one odd battery (I thought it might be near dead since it's mate died earlier). The c-9000 showed this battery capacity to be close to the other two pairs of same brand I had been using so I'd like to throw that into my good battery bag. I probably wont be mixing LSD and HSD, but I can easily see grabbing batteries of different brands if capacities were the same, so I wanted to be sure this was a safe thing to do. Sounds like the worst that could happen is I get a little less run on my light, and that won't affect me since I charge before I need to so I don't have to swap batts on a normal ride. I will probably be less willy nilly about the cells that go into my camera though. I use my 2700mah powerex for that application since I generaly know when I'll be using it and charge up the night before.

 

[uk_caver]

I'm more interested in how the light performs with one discharged cell in, as that's the situation where there's the potential for hammering a cell.

If it doesn't light up, or only gives a dim glow, then you could maybe have some degree of confidence that even with mismatched or differently-charged cells, once the least-good one goes flat, you'd be likely to change cells rather than running the light any longer and actively damaging that cell.

On the other hand, if the light runs at normal (or at least at usable) brightness with one cell flat, then it might be rather easier to damage the lowest-capacity cell out of a mismatched set if the light was ever run until it went dim.

 

[jt4703]

Ahh, I see your point. I'll try to remember to do that next week, it's a long weekend so my charging is done and ready for next week at this point. Shiningbeam shows the Romisen as having constant brightness (not sure if that means constant output though), so I might not notice if just one cell is used up. I know it is noticibly dim as a pair of alkies run down but I haven't let it run down a pair of my rechargables.

 

[Turbo Guy]

Real world testing of two different flavors of AA NiMH cells. The two cells are both old one that are in my very questionalable (for testing) box.
One is a 3 year old LA Crosse 2000 (sure it is) and the other is a 4 plus year old Quest 1400.

I discharged both in the Maha B9000 at 500 mAh to cutoff 0.9V. I let them set a few minutes then discharge again at 0.2A. to get them nice a flat.

Next I place tem in a TerraLux BrightStart 220 EX on high and the light was almost full power. After approx. 25 minutes it dimed to the point that there was no noticeable difference between low and high. Approx. 15 minutes latter the ligh was getting noticeably dimmer on low so I stopped the test.removed the cell and chacked open voltages. The results one cell at 1.12 volts and the other at 0.9 volts.

What does this show? Well to me it shows that very questional,junk cells used in pairs in a flashlight which draws 800 mA on high and 110 mA on low(this one is 110 on low and another one is 250 mA on low) is really not a problem. In normal useage I would never use the light to that point anyway.

I guess in the name of science I could charge these cells and run the complete discharge test in the flashlight. Why not I might just be surprised,I have been before.

Cells charged,open volts 1.42 both cells,installed in light and initial draw 800mA.

In progress results:
30 minutes on high current now at 880 mA , Open voltages Quest(1400) 1.21 / LaCross (2000)1.26

45 min. and noticable dimming on high.
60 min. draw down to 250mA on hi and 80 mA on low. Hi is still noticeable brighter than low and low is brighter than a two cell AA MiNi Mag LED(3 yrs.old) with fresh cells.
Open voltages, Quest 1.09 / La Cross 1.25

90 minutes Hi drain now 140 mA / low 50 mA . On low a little dimmer than AA MiniMag on high still much brighter. Open voltages Lacross 1.25 / Quest .90.
This is a much deeper discharge than I would consider normal. This is my EDC and in normal useage this would amount to several days or more.

2hrs. 15 min. Still brighter on hi than AA LED MiniMag. now 90 mA on hi and 30 mA on low.
Open voltage LaCross 2000 1.23 / Quest 1400 0.04 (yes 4/100 of a volt not 4/10).
test stopped .After 10 min. rest LaCross at 1.25 / Quest at 1.13.
Placed in Manaha C9000 to charge at 1000 cell test volts LaCross 1.67 / Quest 1.73

Quest took a whole 780 mAh to recharge(told you they were tired / junk cells), LaCross 1094 mAh.

OK charge capacity does not indicate real capacity but both cell too approx. 1/2 of their rated capacities. Charger displaying 1.41V for Quest and 1.43 for the LaCross.


To me this shows that it is not critical to have matched cells in many applications. The only time I would run this light down this low would be during an emergency and i would not be concerned with cell damage and besides it would have been used in low mode whenever possible and also turned off whenever possible.

One last test to run perhaps would be a discharge at X rate to 0.9V per cell to see what capacity each cell delivers to that point. IMO it really does not matter as I have proven my point to my satisfaction.

Discharged on B9000 at 800 mA rate Quest 670 mAh / LaCross 1292 mAh.

 

[Lynx_Arc]

Does internal resistance matter, except maybe as a guide to how worn-out a cell is?

If, after a partial discharge from full, it then takes different amounts of charging to get each cell full again (or rather, it takes different amounts of charging until the charger thinks each cell is full), what does that actually say about each cell?

Does the partial or total charge-vs.-discharge efficiency of a given cell reveal much about its state of health?

yes, it matters because it affects the rate of discharge under increasing loads causing uneven discharge levels between the cells themselves and if a cell discharges faster than another and runs out of energy (capacity) it could reverse and/or be ruined.

 

[uk_caver]

Variations in internal resistance won't affect the rate of discharge of different cells in series - all cells will discharge by the same amount, since the current through all the cells is the same.
Two cells in series, with the same actual capacity but different internal resistances will end up discharging at the same rate and going flat at the same time.

 

[VidPro]

Variations in internal resistance won't affect the rate of discharge of different cells in series - all cells will discharge by the same amount, since the current through all the cells is the same.
Two cells in series, with the same actual capacity but different internal resistances will end up discharging at the same rate and going flat at the same time.

but if they are at different voltages due to internal resistance differences they wont be putting out the same wattage 🙂
so if the current is the same,and the capacity is the same , but the voltage is different, then what you got ? hmmm, what you have is two batteries with the same capacity in amps, but not really the same power at all?

there are some perfect examples of that stuff everywhere, batteries that will not output thier capacity under a high load, even if they have huge capacity, but mostly they also wont HAVE very much capacity under a high load ever, so its not as if magically they will wait till the other one is drained out at high voltage, then be the ones still going after the other one died. they are still the ones that will be dead first. even perfectally NEW batteries with different (lets call them) discharge charachteristics .

so as long as the capacities were checked using the same load they will have when used in the device, then the capacity is the capacity, but if they are tested one way for capacity, THEN used a different way in the device, i suppose that would be the internal resistance Gotcha.

so i agree, as long as the capacity IN THAT DEVICE is the same as tested out of the device, then they will go down the same, but stuff dont happen like that when you "Mix Brands and types and batches and dates and such"

 

[VidPro]

To me this shows that it is not critical to have matched cells in many applications. The only time I would run this light down this low would be during an emergency and i would not be concerned with cell damage and besides it would have been used in low mode whenever possible and also turned off whenever possible.

.

sure YOU would take that kind of care.
But
in many Boost flashlights , they will run on .9v, that means one battery is going to be freaking nuked, and generally people who just use stuff, and dont live under a charger, or count thier amps by the hour, destroy a lot of good cells that way. there are Many flashlights out there you can barely tell that the batterys are at that low of voltage, because everybody WANTED great run it down and kill it regulation. batteries DIED for the call of great regulation in lights and bright cheery outputs to the end of the life of both cells.

the more items in series, the more they destroy them too.
i have a few 4 cell devices, and they certannly keep going long after one cell is completly dead, and it really screws up the weak cell. I have to GUARD it like a hawk, because in that device it will run wonderfull, till 1 cell is at ZERO and another cell is very low. so for every 50ma the batts were offset, is 50ma of reverse discharge of one of the batteries.
It certannly shows because they are the little AAAs and they are getting hurt bad, and they cry even 🙂

lots of people have KIDS, you know what those things are 🙂 they sure as heck dont turn stuff off because its dim 🙂

 

[TakeTheActive]

Variations in internal resistance won't affect the rate of discharge of different cells in series - all cells will discharge by the same amount, since the current through all the cells is the same...

This is always true since current is constant in a series circuit.

...Two cells in series, with the same actual capacity but different internal resistances will end up discharging at the same rate and going flat at the same time.

I disagree.

The point I've been trying to make that everyone seems to be overlooking is that the measured CAPACITY is directly related to the INTERNAL RESISTANCE *AND* RATE of current draw.

How can a cell, physically designed to optimally provide a CAPACITY of 2000mAh with an INTERNAL RESISTANCE of N still provide 2000mAh with an INTERNAL RESISTANCE of 2N? When the cell ages, the CAPACITY drops and the INTERNAL RESISTANCE increases. Due to the increase in INTERNAL RESISTANCE, the CAPACITY will be lower since the voltage will begin to drop (larger drop at larger current draw) and the cell will fall off the plateau and hit cutoff.

Now, to throw a monkey wrench into the works. How about pairing a BRAND-NEW 1600mAh @ 100mA cell with low INTERNAL RESISTANCE with a CRAP 2000mAh cell (CAPACITY=1600mAh @ 100mA) with high INTERNAL RESISTANCE? The new 1600mAh cell should be able to deliver over a wide range of currents while the CRAP 2000mAh cell will start fading as the current is increased.

Change the current draw from 100mA to 1600mA and the new 1600mAh cell will still deliver ~1600mAh while the CRAP 2000mAh that measured 1600mAh @ 100mA will now measure lower - let's say 1200mAh @ 1600mA. So, while they were matched in CAPACITY @ 100mA, they aren't @ 1600mA. And, they have different INTERNAL RESISTANCE.

Granted, INTERNAL RESISTANCE isn't the only factor affecting CAPACITY. There could be poorly distributed chemicals, exhausted chemicals, separator damage, etc... (I'm not an engineer, just a hobbyist attempting to form an opinion based on what I've read here in the Archives). But, I believe that two cells of the same designed CAPACITY from the same manufacturer that started out matched cannot age to having the same CAPACITY with different INTERNAL RESISTANCE - IMO, damage must occur.

😕 SilverFox?