![]() ![]() That's when cell equalisation becomes a necessity. What's more, due to manufacturing & chemical & temperature variations between one cell to another, you can't expect all the cells in a string to stay at the same state-of-charge / voltage after multiple charge/discharge cycles. String-cells-1+2+3 in parallel with String-cells-4+5+6 will eventually equalise to the same voltage), BUT within the series string the cells will not equalise to each other by themselves, and you have the same original problem that some cells will reach full when charging, or flat when discharging, before their peers within the series string, and thus be damaged. Multiple strings of series-connected cells that are connected in parallel will equalise with their peers on the overall series-string length (i.e. Multiple single cells can be parallel connected, and they will equalise in voltage, although the current that can flow when they're initially parallel connected can be extreme, and may need to be mitigated with series resistors (and if you're talking about big batteries, then you're talking about beefy big resistors). Installing unequally charged cells in a series string is just plain bad practise - you'll hit over- or under-voltage limits on the over-/under-charged cells way before the others do, and you'll likely damage them. No, a single series string will not equalise the cells in the normal course of charge/discharge, although the degree to which this is a problem and the degree to which it can be dealt with varies by battery chemistry - from not at all, to a reasonable amount. ![]()
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