Originally Posted by HappyMdRSailor
RUDIMENTARY Visualization of parallel v series connection
That's pretty cool but not correct. The parallel drawing is correct but series is not.
When current passes through batteries in series (charging or discharging) it is an equal amount in ALL the batteries. It has to be because there are no exits, what goes in one end must come out the other since there is only one path.
So if you put 50 amps into 3 batteries in series for 2 hours, each battery adds 100 amp hours to its capacity. THIS is where matching of capacity is important because the 100 amp hour battery will become fully charged, the 245 amp hour battery will be only 41% charged and the 65 amp hour battery will be overcharged and gassing excessively as current is forced through it on its way to charging the other two.
The situation is even more critical on discharging.
The 65 amp hour battery will be fully discharged before the other two. When the remaining two continue to force current through the discharged battery you end up reversing the polarity on its weakest cell with -34 volts and rapidly destroying it.
By matching you "hope" they will all discharge uniformly so that they will all be fully discharged at the same time and no cells have enough charge left to destroy another. This NEVER happens and that is why you should never discharge batteries fully so the weakest cell in the chain is fully discharged. When the first cell in the chain is discharged on a 12 volt battery there is 10 volts left to destroy it. But when that happens on a 24 or 36 volt battery there is 22 or 34 volts still available to kill the weakest one.
The chance of matching all 18 cells in a 36 volt battery is much less likely so following the 50% maximum discharge rule
to get maximum life is much more important for higher voltage batteries.