For anyone still following this thread, here is a copy of a PM I received that invites further discussion.
Originally Posted by john61ct
The contention here is that if you parallel 12 volt batteries
, for example, that only the ends of the series chain are at the same voltage and that there may be variations in the charge level of individual cells.
While it is true that the voltage of the individual cells will differ this has nothing to do with being connected in parallel with another battery. The imbalance of cells will be found in every battery, paralleled or not. If there was a need to have cell voltages matching it would be just as important in every battery.
The charge level of a battery and each cell of a battery is measured in AMP-HOURS (that is how many amps can it supply for a given amount of time). It doesn't matter exactly what the individual cell voltage is, because all the current
must go through the cell since it has nowhere else to go, there is only one connection in and one connection out.
This means that each cell gains or loses charge (amp hours) exactly equally independent of what the actual cell voltage may be and when discharging, the battery will fail when the WEAKEST cell becomes tragically discharged.
This process, however, breaks down when a battery cell is fully charged and has run out of electrolytic material to move to the other plate. At this stage putting in more current
cannot increase storage
so the energy is dissipated in "boiling" the electrolyte and creating bubbles. While this is happening other cells will be receiving charge while the bubbling cell(s) remain at full charge. This is what happens when you run an "equalizing" session on a battery long enough for all cells to become fully charged and all making bubbles.
With the arrival of Lithium batteries
, however, there are catastrophic consequences to over charging
or over discharging and balancing cells is crucial. Good Lithium battery managing controls do monitor
the voltage of individual cells and bypass current through cells as needed to maintain balance.