You have a new battery as an energy storage device and of course you want to make sure it lasts as long as possible. But how do you make sure you get the most out of the battery?
Of course, a BMS is vital, as the BMS ensures that the battery keeps working within its limits. Without a BMS, your battery could be significantly damaged in no time at all. Think of an overvoltage or charging while the cell is too cold, which in turn leads to a substantially reduced battery capacity or even cells being broken. But did you know that there is even more that can be done to make sure your battery lasts as long as possible?
Long term storage #
As you may already have heard: it is better to not fully charge batteries when stored away for longer periods. Think about many weeks or months. But what SoC is the best to store the batteries?
Researchers studied the behaviour and lifespan of various types of lithium batteries in 2016. In doing so, they tested the loss in capacity over 10 months, at different SoC and temperatures.
As it turned out, the lower the SoC, the less the capacity degraded. Temperature also had an influence: the battery retained more of its original capacity at 25°C than at 45°C.
Does this mean that it is best to store the battery at a very low SoC, for example 5%? No. Your cell slowly discharges, because of the self discharge and all connected devices like the BMS. At the end of the storage period, you still want a little energy left in your battery. Otherwise the cell could get completely empty, which is far more disastrous for your battery. The good news: the 123\SmartBMS consumes so little, that you can even store the battery at a low SoC for many months.
An example: the 123\SmartBMS consumes a little under 2mA. Together with a 123\SmartRelay, the total consumption is under 3mA. That means that after 9 months, the total discharge is 0.003A x 24h x 31 days x 9 months, which is about 20Ah. I.E. if you have a 90Ah cell, you can leave it at 30% SoC, which is 27Ah. After 9 months, the battery still contains 27Ah – 20Ah = 7Ah.
Tip: when storing the battery, set the “force charge relay” and “force discharge relay” to stay off. All connected power equipment like the power relays will stay in their off position. This will prevent chargers and inverters slowly discharging the battery (quiescent discharge).