Proper battery for high capacity, low drain use.

[alanmalk]

I need a proper battery to use in a 3.7V -10,000 mAH pack, subject to low drain (20 mA or less) over a period up to a year.
Was thinking that a couple of the 5000 mAH cells in the larger sizes, connected in parallel would meet the mAH requirements.
26650 would fit the bill but I note that most (all??) don't come with protection. Since this device will be mostly ignored
I am afraid the batteries could be subject to a 100% discharge/under-voltage condition. I am guessing a battery with
protection is an absolute must in this case.

Perhaps someone can recommend a large capacity battery with protection that I can use in parallel? Fires and explosions
are not an option.

 

[alanmalk]

May have answered my own question. I see some well-known brands at Battery Junction with protection. About double the price - but cheaper than burning down the house.
Hopefully the microscopic drain won't be an issue.

 

[Lynx_Arc]

On low drains a standard alkaline D cell is king you could use 3 of them in series to give you 4.5v perhaps a linear regulator or resistor to drop the excess voltage if needed.

 

[WalkIntoTheLight]

I like that suggestion of using alkaline D cells. At low drain, they should provide over 20,000 mAh. Single-use, but for a year, who cares?

If you go the lithium-ion route, you could use unprotected. The risk of over-discharge comes when you go to recharge them. As long as you're certain to check voltages before recharging again, they should be fine.

 

[LED Monkey]

Do you have limitations of physical size or dimensions of the batteries? there are 21700 5000mah batteries with protection circuits available. Yes D batteries have low self discharge, high capacity and long shelf life but you may want to check on them for the dreaded leakage.

 

[fivemega]

If size is not an issue, Elephant II with 4 parallel 18650 will make a 3-7V, 14000mAh pack.
I don't recommend alkaline cells because they tend to leak.
BTW, don't forget all batteries have either high self discharge or low self discharge. We don't have ZERO self discharge.
If I had a choice, I would go with 10 parallel lithium primary 123A but unfortunately, never seen such thing.

 

[alanmalk]

Do you have limitations of physical size or dimensions of the batteries? there are 21700 5000mah batteries with protection circuits available. Yes D batteries have low self discharge, high capacity and long shelf life but you may want to check on them for the dreaded leakage.

The size constraints are just to keep the battery space consistent with the ePaper display. Or in other words, I probably will limit the battery compartment to roughly 4" X 4" just so I don't have a large container sporting a 1.5" display.

Will investigate the "D" option. Yes, leakage is a worry, and using a LDO to go from 4.5 down to 3.7 may result in unacceptable parasitic drain. Will have to balance all the pros and cons. But the main question - will a very low drain in the 10-20 mA range cause any harm to a rechargeable lion battery? A couple of protected 21700-5000mAH lion's sound attractive (although far and away the most expensive component of the project.)

Thanks to everyone who contributed!

 

[LED Monkey]

Do you mean 10~20 ma draw per year or that much per usage each time you turn it on? The low power drain should not be any problem in itself but if the batteries are usually kept at full or near a full state of charge 4.2v, there will be more battery degradation then if they are stored a lower voltage range like 3.6~3.8v for example. You could charge them up to 4.0~4.1v to lessen any degradation. If you don't mind me asking what type of device are you using? You can keep on the low if you rather not say.

 

[alanmalk]

No problem with identification of the device. A radio receiver turned on for 15 seconds every 5 minutes. 10-20 ma drain when on, nano-amps when off. Using a sparkfun TPL5110 for the timing. No provision for recharging the batteries. Ideal scenario is to remove & charge (or replace if non-rechargable) once per year. With long intervals between inspections - leakage is a serious concern. That's why I am considering a bank of li-ion for 10-20Ah capacity. But I don't want to ruin them by excessive discharge, thus the need for protection. But my primary question comes from all the claims of "10 to 40" amps discharge current. I need the exact opposite. Might consider 3 alkaline "D"s and LDO as suggested above. Possibly needing to throw away the battery holder with the batteries annually.