connecting batteries in parallel or series, myth and theory

phil-news-nospam · 2008-08-07T18:43:07+00:00

I've heard from way back that connecting batteries in parallel is a bad idea.I've heard a couple reasons. One is that it can be hard to make sure thebatteries are loaded equally. Another reason I heard is more complex. Itsays that parallel connection should be done only on a per-cell basis, andthat a series/parallel combination would thus have parallel connections atevery cell ... and therefore multi-cell batteries are bad in this regardwhile single cell (2V) "batteries" are the way to go.Some googling revealed a few web pages that seem to not have much referenceto any parallel connection issues, aside from making sure the batteries arethe same size/capacity.I would think that self-charging (a stronger battery charging a weaker oneconnected in parallel) would not be much of an issue for a batteries thatare intended to keep a float charge, anyway (lead-acid is all that I amconsidering here). If any battery has a problem where it can't take acharge and could be a hazard if charged, then it seems one would have abigger issue by that alone than anything related to wiring them in parallel.Maybe there are issues when the _number_ of paralleled batteries is high?Series connection would _seem_ to be more of a problem, but clearly isn't ashow stopper at common voltage levels (12 to 48). What I refer to when I saythis is the risk that a single weak cell in the series woould be effectively"reverse charged" by the "brute force" of the high voltage series circuitforcing the current in the reverse direction than a charging current. On theface of it, this risk seems like one that, if it could happen, would happenon even a small a voltage as 6 volts (3 cell). But maybe for lead-acid therisk is merely depleting the bad cell to zero and destroying it and nothingmore?What risks ... to the batteries themselves ... exists in a very high numberof cells in series wired for very high voltages (120 to 600 volts for example)?I remember running across, a few years ago, a very large DC...