Rechargeable D-cell batteries - could use some advice please

Hi,


You folks seem to be the rechargeable battery gurus, so hopefully it's ok to post this here.


I inherited a project at work that involves data recorders, each powered by 4x D-cell NiMH 1.2V batteries. We're talking 500+ batteries. The lab has literally bins full of three types of D-cell batteries:


IMEDION 9500 mAh
POWEREX 11000 mAh
POWEREX 9000 mAh


Some have been used in the field before, some are new. Batteries used in the field have spent at minimum 2-3 months, sometimes cumulatively 8-12 months (I'm not sure) in weatherproof enclosures exposed to typical southeastern US conditions (heat and humidity). The recorders stay in standby mode for days or weeks, then activate for short periods over 60 days.


I have some questions about maintaining this rather pricey stock of batteries. The previous guy left before I started, and any way, I want to implement best practices for storage and maintenance so these batteries continue to perform properly in the field. If I need to buy new batteries, or new testing/charging equipment, that can probably be worked out.


Testing:
We have a ZTS Pulse Load Multi-Battery Tester MBT-1. It seems to work ok, but would a fluke meter be a better option? (I admit, I kind of just want a fluke to have around, but only if I have a legit need). The MBT-1 gives a 10%, 20%, 40%, 60%, 80%, (>80%) reading, but I'd like to know if the batteries are charging properly and anticipate failures, so I can take them out of rotation. I'd rather toss a semi-questionable battery than risk a failure in the field.


Some of the batteries have brown discoloration of the paper tops, which I am assuming is chemicals leaking from the battery. I think those should be disposed of, correct?


Charging:
We have several Maha PowerEx MH-C808M Charger for Eight AA/AAA/C/D NiMH/NiCD Batteries. I need to find a manual to understand the soft vs rapid charging modes. Also, I'd like to know if it's ok to charge the various mAh batteries mixed up on the charger or if I should only charge like-batteries.


Should I do some sort of topping off between deployments? They'll come back to me drained in, say, April. Then they won't be needed again until December or January. Should I recharge in April, then top them off in Dec? What's best practice?




Deployment:
Each recorder takes four batteries. I'm assuming they ought to be charged to the same level (they'd all be topped off). Can I mix batteries in devices, or should I stick to all four being the same type in any given recorder?




Storage:
Some of the batteries are stored on their ends in heavy plastic trays, while many others are dumped into bins. The latter gives me the heebie-jeebies, and makes me worry about fire hazards. I plan to - at the very least - have them all stacked up on end so they can't touch the neighbor's terminals. Should I be worried about venting gas during storage or charging, or is that just Lithium chemistry batteries?




I think that's enough questions for now. I appreciate y'all taking the time to read through and help me out.

Testing -
it would be better to get a combine charger/tester that has the capability to test the cells for you, you can get a lot more info about the cells than the MBT-1 tester provides. The two useful test that you should have available to run are a discharge capacity test to actually measure the milliamp-hours capacity for each cell and an internal resistance measurement (milli-ohm) that is a good indication of the overall health and remaining service life for the cell. Worn cells with higher resistance might still be able to deliver acceptable milliamp-hours capacity but only at a low discharge rate. You might want to figure out the peak amp draw from the meters. It is likely that the peak draw is fairly low and they only have 4 big D cells to provide a large milliamp-hours capacity to pull from over a long time? I have a "Miboxer" brand charger that I really like measuring/maintaining my battery collection but the one limitation is that it only runs capacity test on a single circuit, it would take over a year to check all your 500+ cells on a single circuit! Search around and/or get recommendations for such an analysis charger that is able to test multiple cells at the same time.

Charging- the "fast" 2000 mA charge rate available from the MH-C808 is still fairly slow for a large 9000 mAH battery (C/4.5 charge rate for such a cell). A D-Cell in good condition should have no problems with accepting a 2000 mA rate. If you are only deploying the batteries a few times a year, I would worry less about the wear from each charge, the cells will likely die from old age long before you have reached the limit of available charges (somewhere around 500 times). It looks as if your MH-C808 charger has 8 separate circuits, should be no problem to mix different cell types on that charger.

I would suggest giving each cell an ID # label, testing each of them for internal resistance and mAH capacity and keeping a log book (or spreadsheet) of the test results and usage. With test results available, you can grade the cells and group them into similar performance categories so that the 4 cells used for each recorder are same type and capacity to get the most consistent performance. Biggest problem you will have with such a large fleet of cells is from the old worn cells with minimal life, if the dead/sick cells are mixed up with your good cells it is very hard to predict if the battery pack will last and provide acceptable performance. Much better to identify and cull out the worn cells so you can confidently create matched sets of good functioning cells for each pack.

Hello NPS,

Welcome to CPF.

What a project...

The advantage of the ZTS tester is that it measures voltage under load then compares that to a look up table of similar cells. If you know the maximum load of your deices, you can do something similar by measuring the voltage using your Fluke while applying the load. This is a good reason to get the Fluke.

The ZTS works great as a survey tool, but you need a little more than that.

The discoloration is worth noting, but performance is a better indication of cells that are failing.

To define performance you need to identify the cells, test each one and log the results. You will end up with voltage under load and capacity. When the voltage drops a "significant" amount, recycle the cell. When the capacity drops to below roughly 80% of its initial capacity, recycle the cell. You have the disadvantage of not knowing the initial capacity of the cells but you should be able to work around that.

The 808 is a great charger but you need an analyzer to give you capacities.

You can mix and match when using the 808. Each channel is independent. Soft charging for D cells is at 1 amp. Normal charging for D cells is at 2 amps. I would suggest using Normal charge rates for the bulk of your use.

When using multi cells it is best if the cells are matched on capacity. You can look through your test records and put together "packs" of cells to use.

The rate of self discharge can be measured. Charge the cells up and store them for something like 6 months. Then test the remaining capacity. This will give you an idea of the rate of topping off needed to meet your needs.

It sounds like you have a good handle on storage. Anything is better than just dumping the cells in a bin...

The manual for the 808 can be found here.

Tom

I have some Imedion D batteries. I like them because the self discharge is fairly low. They claim that they hold 85% after a year which is accurate from my experience. The Powerex 1100 mAh I have also tried and found the self discharge to be much quicker. The ones I have are white with the red stripe at the positive end. The third the Powerex 9000mAh I have no experience with.


Of course try and match battery capacity and type when you are using them in series. Also topping off NiMh batteries is fine. I don't see anything negative to doing that.


I have a ZTS tester also and I find it not very useful for NiMh batteries if you want see the percentage of charge between about 85% and 15%. It's not the tester's fault it's the nature of the chemistry. IMHO the voltage and voltage sag under load is just so close between 85% and 15% that the tester can't accurately detect the difference.


It would be great if you could test the capacity of all of them to weed out the duds. But if you have over 500 of them that may not be a practical option. There lots of testers that will check capacity but very few will handle D size cells. Any ones that have physical visual damage just discard them, it's not worth the trouble. The Skyrc Mc3000 can test two D batteries at a time, but t's a little pricey and not turn key to operate but I will try to help with questions about it's settings. But If you can recover 10 or more Imedion D cells it just paid for itself.

Frank

The Skyrc Mc3000 looks like a great suggestion. Even if it only comes configured to fit 2x D cells in the two outer slots, you could easily add wires on the two crowded inner slots to connect them to external battery holders so that you can run the analyze function on 4 cells simultaneously.

I may be wrong, but seems the only analyzing charger capable to serve 4 D cells at once is Xtar Dragon. All others accept D cells in 2 slots out of 4 or don't accept them at all.

I myself was forced to buy 2 Xtar SV2 chargers to take care of 4 D cells at once.

The Xtar Dragon VP4 looks like it does everything I might need, although with only four ports, it might take a while. I'm not clear on how long a testing cycle will take, but I have 6+ months available before the batteries are needed, and I can probably buy 5 or 10 testers if needed.

I have run all the batteries (about 500) through the MAHA Powerex MH-C808M charger at this point. My intention was to get them topped off prior to doing any testing. In the process, I found about 100 that had no apparent charge and were not recognized by the charger. I set those aside. I'm not sure if it's possible to recover the cells (the Xtar Dragon appears to have an option to try). And if they're recovered, would they still be as reliable as non-recovered batteries when deployed in the field? If not, I'm going to toss them.

Interestingly, all but about 2 or 3 of the 100 completely dead batteries were Powerex 11,000 red-tops.

(I'm not sure if my previous comment is being moderated or was lost. I'll summarize my last post)

I charged all 450 or 500 batteries on the Maha PowerEx MH-C808M Charger. About 100 were not recognized by the charger and did not charge. The other tester suggested they were completely flat. Should I toss them or try and recondition them? If reconditioned, will they ever be as trustworthy as cells that have never gone completely dead? (If not, I'll toss them).

The Xtar Dragon VP4 charger / tester seems like it can do all the recommended tests that y'all suggested, working on 4 batteries at a time. I plan to number the cells, test them, and keep a log to track batteries on their way to failure.

I know I'm forgetting something from my earlier post. I'll probably remember as soon as I hit submit. lol

If your chargers recondition cycle does not help the dead cells, you can first try to zap a small amount of charge back into them so that the charger will at least recognize them a batteries instead of bricks. Ive used a 12v, 5 amp automotive charger to quickly zap dead cells for several seconds (Frankenstein style) but you could likely do the same thing using a couple of your good fully charged D-cells connected in series to deliver a zap to the dead cell or else use a 18650 Lion if you have one available. After just a few seconds of high current, the charger will usually then recognize and start either a recharge or condition cycle. No guarantee that such resurected cells will revive to be good as new, but if you get a testing charger, you should be able check the internal resistance, capacity and then check their longer term self-discharge stability to asses their health for further use.

As you may notice, both your posts are here

NiMH cells are not so obvious as Li-Ion, but I guess high internal resistance might be a sign of wear or poor condition.

NPS said:

The Xtar Dragon VP4 looks like it does everything I might need, although with only four ports, it might take a while. I'm not clear on how long a testing cycle will take, but I have 6+ months available before the batteries are needed, and I can probably buy 5 or 10 testers if needed.

I have run all the batteries (about 500) through the MAHA Powerex MH-C808M charger at this point. My intention was to get them topped off prior to doing any testing. In the process, I found about 100 that had no apparent charge and were not recognized by the charger. I set those aside. I'm not sure if it's possible to recover the cells (the Xtar Dragon appears to have an option to try). And if they're recovered, would they still be as reliable as non-recovered batteries when deployed in the field? If not, I'm going to toss them.

Interestingly, all but about 2 or 3 of the 100 completely dead batteries were Powerex 11,000 red-tops.

Click to expand...

If I am not mistaken, the 11,000 mAh powerex cells are not low self discharge and will lose most if not all of their charge in a few months....they pretty much need to be charged just prior to use and recharged frequently if kept in storage. If the charger is not taking them due to low Voltage they have over discharged - they may still be good if you zap them briefly with another charged cell in parallel (neg to neg, pos to pos) but chances are they are toast if they have been sitting at 0 Volts for a long time. If the charger is rejecting them due to high internal resistance, than they are definitely toast.

Hello NPS,

If you have infinite time...

It is fun to play with "dead" cells and try to bring them back to life. Unfortunately it isn't extremely productive. Sometimes it works but if you assume none will be revived, you will have realistic expectations and may be pleasantly surprised from time to time...

The rest of the story is that if you happen to recover a few cells, they frequently will have higher rates of self discharge and an extreme low cycle life.

I like your idea of just recycling them.

Tom

SilverFox said:

Hello NPS,

If you have infinite time...

It is fun to play with "dead" cells and try to bring them back to life. Unfortunately it isn't extremely productive. Sometimes it works but if you assume none will be revived, you will have realistic expectations and may be pleasantly surprised from time to time...

The rest of the story is that if you happen to recover a few cells, they frequently will have higher rates of self discharge and an extreme low cycle life.

I like your idea of just recycling them.

Tom

Click to expand...

I think I agree. I was waiting to check the bad cells out on my new XTAR Dragon VP4+ charger. So, these particular NiMH D cells were not taking a charge on the other charger. I tested them with the leads on the Dragon VP4+ charger and it was reporting 0.00 for voltage and resistance. Plugging them into the charger gave me 'ERR' on the display. I switched to refresh mode, just to try it, and I still have 'ERR'. I'm going to conclude the cells are toast, correct?

I have about 110 of these bad D-cells. If they're dead and gone, I'll recycle them. If they can be recovered, but will never be trustworthy, I'll likewise recycle them (I cannot tolerate failures out in the field). But they're like $18/ea, so I want to be sure I was thorough before I dispose of them. That's like $2000 in batteries I'm about to toss out. Eek.

Did you try to "prime" them with another healthy battery: "+" to "+", "-" to "-" for a couple of seconds? Of course, you should test them first to be sure they aren't short inside.

NPS said:

I think I agree. I was waiting to check the bad cells out on my new XTAR Dragon VP4+ charger. So, these particular NiMH D cells were not taking a charge on the other charger. I tested them with the leads on the Dragon VP4+ charger and it was reporting 0.00 for voltage and resistance. Plugging them into the charger gave me 'ERR' on the display. I switched to refresh mode, just to try it, and I still have 'ERR'. I'm going to conclude the cells are toast, correct?

I have about 110 of these bad D-cells. If they're dead and gone, I'll recycle them. If they can be recovered, but will never be trustworthy, I'll likewise recycle them (I cannot tolerate failures out in the field). But they're like $18/ea, so I want to be sure I was thorough before I dispose of them. That's like $2000 in batteries I'm about to toss out. Eek.

Click to expand...

Since you need these cells to work properly, I would recycle any that are over discharged (under 0.5V) or have high internal resistance. I would also ditch any old high self discharge cells and only use good fairly fresh low self discharge cells. Test the rest and get rid of anything that is below 80% initial capacity. Keep in mind that even rechargeable batteries don't last forever and will need to be replaced even if they are unused after a certain number of years. Over discharging kills NimH cells so they will need to be charged ideally every 6 mo. or so even in storage and topped off again before they are put in service.

vadimax said:

Did you try to "prime" them with another healthy battery: "+" to "+", "-" to "-" for a couple of seconds? Of course, you should test them first to be sure they aren't short inside.

Click to expand...

I have put some of the batteries that were reading 0.00 V and 0.00 mOhms onto the Dragon Charger and attempted to recover them. Two out of the 40 I tried this with started charging. The rest gave me a 'ERR' message. But let's face it, I'm never going to trust those batteries again, even if I recover them. I think this backs up my decision to recycle them.

xxo said:

Since you need these cells to work properly, I would recycle any that are over discharged (under 0.5V) or have high internal resistance. I would also ditch any old high self discharge cells and only use good fairly fresh low self discharge cells. Test the rest and get rid of anything that is below 80% initial capacity. Keep in mind that even rechargeable batteries don't last forever and will need to be replaced even if they are unused after a certain number of years. Over discharging kills NimH cells so they will need to be charged ideally every 6 mo. or so even in storage and topped off again before they are put in service.

Click to expand...

My maintenance plan is as follows:
1. Recycle any batteries that are over discharged (V < 0.5 V).
2. Recycle any that have high internal resistance (is >100 mOhms reasonable?)
3. Charge remaining batteries (top them off).
4. Test charged batteries and log these parameters: Voltage (V), Internal resistance (mOhm), Charging capacity (mAh), and Discharge capacity (mAh).

(Here's where I'd like feedback on my cutoff values for freshly charged batteries
Factory Specs: Voltage = 1.2V; Charge Capacity (varies by battery type, 9,500, 10,000, or 11,000 mAh)

Recycle if a freshly charged battery meets one of these conditions:
Voltage < 1.1 V
Internal Resistance > 100 mOhm
Charge Capacity <85% factory specs
Discharge Capacity <85% factory specs

5. After 4 months, recheck voltage and internal resistance. Recycle if they exceed above tolerances.
6. Recharge all batteries.
7. Test charged batteries and log these parameters: Voltage (V), Internal resistance (mOhm), Charging capacity (mAh), and Discharge capacity (mAh).
Repeat on a 4 month rotation


How does that sound for a plan? Are my cutoff levels appropriate? Any suggested changes?

I do want to ultimately replace all the 11,000 mAh batteries with the 10,000 mAh ones, because they seem to be by far the worst for self discharge and failures. About 100 out of 650 batteries were bad upon initial examination, and 98% were those red-top 11,000 mAh POWEREX batteries.

Is monitoring these parameters sufficient to ensure battery health, or should I plan on a hard age cutoff, and recycle batteries older than a certain number of years? I have about 425 that are of unknown age (I'm assuming from 2009) and another 175 I think are from 2017.

i damaged so many power tool nicd by storing them fully charged, once i started discharging them to 20% for storage, they run longer. same with nimh cells, they also like when you cycle them once in a while.
i used several different tenergy nimh D, the blue ones did not last long, permum ones and centura lsd lasted much longer.

NPS said:

I have put some of the batteries that were reading 0.00 V and 0.00 mOhms onto the Dragon Charger and attempted to recover them. Two out of the 40 I tried this with started charging. The rest gave me a 'ERR' message. But let's face it, I'm never going to trust those batteries again, even if I recover them. I think this backs up my decision to recycle them.



My maintenance plan is as follows:
1. Recycle any batteries that are over discharged (V < 0.5 V).
2. Recycle any that have high internal resistance (is >100 mOhms reasonable?)
3. Charge remaining batteries (top them off).
4. Test charged batteries and log these parameters: Voltage (V), Internal resistance (mOhm), Charging capacity (mAh), and Discharge capacity (mAh).

(Here's where I'd like feedback on my cutoff values for freshly charged batteries
Factory Specs: Voltage = 1.2V; Charge Capacity (varies by battery type, 9,500, 10,000, or 11,000 mAh)

Recycle if a freshly charged battery meets one of these conditions:
Voltage < 1.1 V
Internal Resistance > 100 mOhm
Charge Capacity <85% factory specs
Discharge Capacity <85% factory specs

5. After 4 months, recheck voltage and internal resistance. Recycle if they exceed above tolerances.
6. Recharge all batteries.
7. Test charged batteries and log these parameters: Voltage (V), Internal resistance (mOhm), Charging capacity (mAh), and Discharge capacity (mAh).
Repeat on a 4 month rotation


How does that sound for a plan? Are my cutoff levels appropriate? Any suggested changes?

I do want to ultimately replace all the 11,000 mAh batteries with the 10,000 mAh ones, because they seem to be by far the worst for self discharge and failures. About 100 out of 650 batteries were bad upon initial examination, and 98% were those red-top 11,000 mAh POWEREX batteries.

Is monitoring these parameters sufficient to ensure battery health, or should I plan on a hard age cutoff, and recycle batteries older than a certain number of years? I have about 425 that are of unknown age (I'm assuming from 2009) and another 175 I think are from 2017.

Click to expand...

Sounds good.

The internal resistance is a bit of a moving target as it varies with state of charge, you will be able to judge better which ones are too high compared to the rest and new cells.

For your application , I would definitely recycle the ones from 2009. I would also get rid of any that are of the high self discharge because they may go dead during your data recording in the field. Newer low self discharge types should be able to hold a good charge for 6 + mo.

NPS said:

2. Recycle any that have high internal resistance (is >100 mOhms reasonable?)

Click to expand...

The internal resistance does relate to the overall health of the battery but I think that the criteria of > 100 mOhms is likely more conservative that necessary, meaning you would potentially be recycling batteries that are still fit for service. Low resistance cells are needed in high energy drain applications (super bright flashlights and such) but if your remote monitors are not ever pulling high current levels from the batteries during use then the mAH capacity and the long tern self-discharge rate should probably be weighted more than the internal resistance.

More of that, some batteries behave I mean when discharged they may display > 100 mΩ, but once charged they show some 60 mΩ of internal resistance? And now what?