how about 21700 4500 mah battery vs energizer l91? im still deciding on my survial cells

raggie33

*the raggedier*
Joined
Aug 11, 2003
Messages
10,913
at aroiund 1/10 a amp how many l91s would it take to have the runtime of one 21700 cells?
 

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
10,833
Location
Tulsa,OK
A 21700 at 3.7v x 4500mah is about 16.7W. An L91 at about 1.5v x 3500mah is about 5.3W so it would take approximately 3 L91s to equal the 21700 at that current level I calculate. LIkely the 21700 would take up less space.
If it were me doing the bug out emergency etc bag I would likely have 1-2 AA lights with a few batteries and the rest 18650 or 21700s and a decent size power bank or two. The rechargeables and power bank likely would last for days even weeks before you have to resort to the AA stuff and the L91s would stay good for 20+ years unused unlike alkaleaks that I believe have increased chances of leaking as they age, and if they do leak they are worthless likely to use.
 

Hooked on Fenix

Flashlight Enthusiast
Joined
Dec 13, 2007
Messages
2,200
21700s can get up to around 5 amps and start at 4.2 volts. I think AA lithium’s are around 3 amps. You need nearly 3 to get the same voltage as one 21700. 21700s can sometimes handle over 15 or 20 amps whereas lithium primaries max out at 3 amps each (21700s have half the resistance as 3 lithium AAs.) Use three together to get around the same voltage and you get 9 amps. I would estimate you’d need 5-6 lithium AAs to match a 5 amp 21700 or about 12 AA alkalines.
 

Olumin

Enlightened
CPF Supporter
Joined
Sep 20, 2020
Messages
658
Location
"...that famous Texas part of Hamburg"
Rechargable Li-ion batts are generally not ideal for long term storage, and also handle temperature worse then li primaries. If you plan on storing them for emergency use (which I infer from the title), I suggest using lithiums despite lower energy density/drain.
 

Poppy

Flashaholic
CPF Supporter
Joined
Dec 20, 2012
Messages
6,142
Location
Northern New Jersey

uk_caver

Flashlight Enthusiast
Joined
Feb 9, 2007
Messages
1,404
Location
Central UK
When trying to compare cells with different voltages, compare Watts and Watt-Hours--not Amps. Watts = Amps x Volts
Wasn't the 1/10Amp just indicating the expected drain current of the cells?

Though you're generally right regarding Watt-hours being the best measure, that does rely on what is being powered using the voltage/current efficiently - if using 3x L91s in a 3xAA light (or a 21700 in a single-cell light) which had a linear driver, runtime would be dependent on single-cell Ah, not total-cell Wh.
 

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
10,833
Location
Tulsa,OK
Wasn't the 1/10Amp just indicating the expected drain current of the cells?

Though you're generally right regarding Watt-hours being the best measure, that does rely on what is being powered using the voltage/current efficiently - if using 3x L91s in a 3xAA light (or a 21700 in a single-cell light) which had a linear driver, runtime would be dependent on single-cell Ah, not total-cell Wh.
The only thing specific we have to go on here is two battery types and specs and 100ma current drain which I have to consider is for either option. I agree that the power output at 100ma for a single 21700 vs L91 is about 3x as much but we cannot assume much based upon the limited information given to us. 100ma drain is plenty in even a 1AA light to power out lumens in a case where there is no power and the likely light pollution is minimal. Personally I would opt to go with 18650 based lighting over 3AA when 21700 solutions are not available. I'm not an overall fan of the battery type for general purpose as there are too few options for its use right now and plenty for 18650s. I assume in the future that will change perhaps we may even see single cell 21700 powered lanterns and work lights that use replaceable batteries in them. Even with the higher amount of power that a single cell can contain in it the 21700 isn't mainstream yet but gaining in popularity. There may be new types of go to batteries on the horizon that may replace both sizes in many uses.
On the other hand I think one of Energizers patents on the L91 runs out next year perhaps that will lead to competition and cheaper offerings in that category.
 

Poppy

Flashaholic
CPF Supporter
Joined
Dec 20, 2012
Messages
6,142
Location
Northern New Jersey
at aroiund 1/10 a amp how many l91s would it take to have the runtime of one 21700 cells?
I took this question to mean similar run time, at similar output levels.

In recognizing that one can not draw a straight-line comparison, given that LEDs perform differently at different voltages, and the sum of the voltages of one, two, or three L91's will not equal the voltage of a single 21700 cell.

Therefore I once again offer to meet those conditions, that it takes a little more than 3 L91 cells to compare to a single 5000 mAh 21700 cell.
 

vicv

Flashlight Enthusiast
Joined
Mar 22, 2013
Messages
1,387
Location
Southern Ontario
Also an l91 is good for about 3A. A 21700 is good for 30A. Big difference. But if the op is looking for strictly storage, then I have to give the nod to the l91 cells. But I would still say that cr123a's are better. The actual chemistry of l91 I think has some strong advantages but you need two of them to get the same voltage which makes it in my opinion less desirable
 

vicv

Flashlight Enthusiast
Joined
Mar 22, 2013
Messages
1,387
Location
Southern Ontario
Unless he's running an analogue clock he's going to need more than that. And I was talking about differences. Not necessarily exactly as op said. Also he's trying to decide on his survival selves. So everything is relevant
 
Last edited:

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
10,833
Location
Tulsa,OK
Unless he's running an analogue clock he's going to need more than that. And I was talking about differences. Not necessarily exactly as op said. Also he's trying to decide on his survival selves. So everything is relevant
While that is likely true, unless you directly query him about what his uses are and then reply to that information the reality could be exactly as he is asking or something completely different..... we don't really know.
I've found many people in power outages that they consider lengthy use low modes on lighting and even in a boosted single AA light 100ma of power from the battery can give you a decent amount of light which can suffice. With L91s and 21700s both are lower internal resistance than alkaleaks such that going to 500ma should favor the 21700 but not extremely it may take an additional L91 to match the power curves of a 21700 under increasing load but 3 L91s is a decent starting point 4 would likely give you some headroom for a boost circuit at moderately higher currents.
I'm not anti AA, especially single AA but when you start to add them in series unless you use L91s you can have issues with them. Nimh can be unbalanced in capacity and internal resistance and over time performance can lag badly while alkaleaks can leak and if treated harsh leak even more often while L91s are very good overall the cost of them in use adds up vs a 21700. I'm all for using them for backup purposes but I would lean heavily on the 21700s for most purposes even the heavier tasks as they (and 18650s) are the most power dense and less hassle free battery choice there is right now and if you start piling 16 L91s up (or more) and you can get by with 4-5 21700s instead it makes for more room for other items in your kit. I'm thinking unless a person finds themselves unexpectedly without power for more than a week a half dozen 21700s and a decent power bank or so should easily suffice and if that doesn't you can then find a way to buy AAs or.... charge up some 21700s somewhere that has power as most places you are considering buying from will likely have power.
 

vicv

Flashlight Enthusiast
Joined
Mar 22, 2013
Messages
1,387
Location
Southern Ontario
Agreed. I can only presume though from the thread title it's for emergency use. The long term storage of the different chemistries is an important consideration.
I believe the op mentioned .1A so losses from internal resistance wouldn't be factored into the final capacity. A simple look through HJKs reviews/graphs will show around a 40% capacity advantage for a top 21700 compared to 3x l91 in series so I don't think the only criteria is mAh or only a .1A draw hence why I mentioned other considerations
 

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
10,833
Location
Tulsa,OK
Agreed. I can only presume though from the thread title it's for emergency use. The long term storage of the different chemistries is an important consideration.
I believe the op mentioned .1A so losses from internal resistance wouldn't be factored into the final capacity. A simple look through HJKs reviews/graphs will show around a 40% capacity advantage for a top 21700 compared to 3x l91 in series so I don't think the only criteria is mAh or only a .1A draw hence why I mentioned other considerations
Long term storage of any rechargeables requires either occasional recharging or recharging prior to seasons where there would be possible bad weather etc. This is why L91s are good and vs CR123s they can be used in a lot more items than them are easier to source also and many devices using AAs can use alkaleaks (ugh) in an emergency you could go rob all your remotes and clocks and so on for AAs.
 

Poppy

Flashaholic
CPF Supporter
Joined
Dec 20, 2012
Messages
6,142
Location
Northern New Jersey
Am I reading these graphs correctly?
If so, it appears that 0.1 amps (100ma) will deliver about 40 lumens.

The following graphs were taken from the Cree XPG Datasheet.

considering that 130 flux is the base @ 350 ma.

1634940474081.png


100 ma should output 25% of 130 flux or about 40 lumens.

1634940335888.png


and the LED should pull 0.1 amps or 100 ma, when the voltage is at 2.75 volts without regulation.
1634940642132.png
 
Last edited:

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
10,833
Location
Tulsa,OK
Am I reading these graphs correctly?
If so, it appears that 0.1 amps (100ma) will deliver about 40 lumens.

The following graphs were taken from the Cree XPG Datasheet.

considering that 130 flux is the base @ 350 ma.

View attachment 18547

100 ma should output 25% of 130 flux or about 40 lumens.

View attachment 18546

and the LED should pull 0.1 amps or 100 ma, when the voltage is at 2.75 volts without regulation.
View attachment 18548
If you are using a 1.5v source with a boost circuit you will probably get about 15 to 20 lumens using that much current from the battery. Plenty useful in a power outage to conserve battery power where there is little light pollution.
 

fuyume

Newly Enlightened
Joined
Jun 25, 2021
Messages
181
The easy answer is a mix of AA and 21700 is a good setup. LiFeS2 L91s are excellent for high current drain, wide temperature tolerance, storage life, and availability, plus any old AA can still be used in a pinch.

21700s are best for frequent usage, high capacity, extremely high current drain applications, but as with all rechargeables, you have to use it or lose it.

21700 is the best single-cell solution, AA is the most widely available. I use both, and so should you.
 

raggie33

*the raggedier*
Joined
Aug 11, 2003
Messages
10,913
i sometimes even use less then 100 ma sometimes 2 or 3 ma on my sofirn when i lower the start ramps level.
 

Latest posts

Top