As my season comes to a close (water gets really hard where I foil😀) I’ve been thinking of how to store my battery in a manner that best protects it. I am also curious about what others do in regard to what they feel is a viable max charge and discharge V.
As far as I know Liion battery cells are rated for a V range of 2.5 to 4.2 as absolute MIN and MAX values and a long term storage V of 3.0 to 3.5 depending on what the source of the info is. (Lot of varied opinion on this). Those opinions also touch on storage temperature and that factor also varies.
The pack value is the cell V value multiplied by the S count so in simple terms a 10S battery pack has a theoretical range of 25V to 42V. 12S would be 30 to 50.4V and so on.
I like to be a little conservative so I would only charge that 10S pack to 41V and stop using it at 31V (using VESC absolute cutoff limit). It is also my opinion that once V drops to ~30V the performance of the motor starts to be impacted so there is no point in risking the battery by draining it lower.
Looking forward to hearing sage advice or correction(s) to my admittedly basic understanding.
Storage 3.75V is ok. If you don‘t have a bms connected, they should not discharge much until spring.
I charge to 4.15V and discharge to 2.97V (under load). When the battery cools down, the voltage climbs above 3.1V without load. You could go lower but there is not much capacity left from 2.9 down to 2.5V and as VESC only throttles and stops on total voltage, there needs to be some room for out of balance rows.
Do you have a recommendation or opinion for temperature of the storage location?
It depends on the cell you’re using what voltages are considered limit voltages, an example is lipo pouches that should not be as low as 2.5V, but this is the lower limit for many 18650 cells from the manufacturers - same goes for storage voltages.
This is my first foiling season so don’t have a depth of knowledge, certainly not on LIPO or pouches. It is my impression that Liion cells are more commonly used by the participants in this forum.
I started with 18650 cells and have recently acquired some 21700 cells. The spec sheets for both state 2.5 and 4.2V so that is the source of my numbers above and is why I tried to limit my topic to things I actually have used myself.
You have been at this a lot longer than most so would appreciate what you consider best practice for the type of cells I have.
Depends on the cell and how many cycles you want out of your pack - there’s no general truth even for cylindrical cells.
I normally use my packs between 3.3V (because there is very little capacity left and they dive quickly after this voltage) and 4.15V (to get some headroom to overcharging). If i want to go max i charge to 4.2V
I store at 3.7V since that’s recommended by the manufacturer for the cells i have now.
Do you long term (> 1 month) store at room temp or something colder or warmer?
It doesn‘t matter that much, I store mine in the basement which is between 10 (winter) and 25 degrees (summer). Should not be below zero, better keep them above 5 degrees C.