BMS for Lithium ion battery
Selecting BMS is not only dependent on the battery amps or Ah. It also depends on several other parameters like maximum charging current, maximum discharging current of the battery, peak current i.e. by what rate we can charge or discharge our battery like 0.5C or 0.8C or 1C. This capacity C rating is provided by the battery provider.
So it is better to know the maximum charge and discharge current we want from our battery.
Finally, yes you can use 40 Amp BMS but on the other hand you can save your money while choosing BMS by considering above parameters.
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