we get asked lots of questions on how to take care of the battery pack. It's a huge and costly component of your board and with a few tips and tricks, you'll make sure to extract the most our of it.
So while you may think that keeping the battery level between 30% and 70% is the best way to maximize its life, it's not the case. Indeed, in theory, that's true. In practice, it's not. Here's why.
For starters, the balancing of the cells happens at the very end of the charge cycle, when the amps pumped into the pack are greatly reduced and it basically trickle charges to make sure the cells are all balanced (i.e. they all have the same voltage).
However, this has its limits since it's done through the BMS (battery management system). If a cell is too far down in voltage, i.e. if for some reason one of the cells in a P pack is too low and keeps getting lower and lower as you keep the pack between 30% and 70% (and "why" this cell is running off like a lost sheep is a whole other discussion), then the BMS won't suffice to balance the cells and 1 of your P packs will always be unbalanced, dragging the whole pack down with it. Packs are simple, they are like herds - not faster than their slower member.
The result of this is very simple - when the rest of your pack is still at 50%, this single cell at say 20% will make the BMS kick in to preserve cell life (and battery pack life) and the shut offs will activate. To be clear, your board will enter into soft then hard cut off while your app shows 40% or 50% or 60% charge. Total bummer.
So while you might be maximizing the theoretical life of your pack by keeping it between 30% and 70%, the result is you risk unbalancing one of your cells to a level the BMS could no longer handle. Then, all is not lost, but to rebalance your pack safely and efficiently (without jerry-rigging it which might do more damage to the cells you fought so hard to preserve), you need a fancy balance charger that costs a small fortune. Is it worth the investment? You do the risk assessment and the math but in our mind it's a "risky" investment.
Finally, when storing the board for long periods (like winter, or a few weeks), keep the battery around 70%.
The Lacroix Team