"Meindert Sprang" wrote in message
...
snip

Obviously you don't know what you are talking about.
With such a setup you achieve two things:
1) one battery will always be drainen slightly more than the other.
Correct (although it obviously depends on usage).

2) that same battery will alway be charged a little less than the other
because the charger measures the voltage across both batteries in series.
Incorrect. The charger measures the voltage across both batteries in series.
The voltage it sees is the result of both batteries being there, not the one
with the highest or lowest charge. The charger will charge until the
voltage across the two batteries reaches the correct level. Whether
individual cells (and being in the same case or in different cases makes no
difference) took a longer time to get up to par simply doesn't matter.

So eventually that battery will be in a continuous state of being empty.
Imagine what happens when you start the enginge or put another heavy load
on
a series of batteries where one of them is empty: the empty one will be
charged by the full one, but with reverse polarity.
This is not what happens, and I cannot imagine what scenario you have in
mind that could create this situation. Have you ever replaced one battery
in a two-battery 24v system with a brand new battery? What happened when
you started the engine? I have and I can tell you the answer - the
uncharged battery gradually charged, as you would expect.

Have you ever disassembled a broken battery pack of some device? In 99% of
the cases you will find all cells in perfect condition (charged and all)
except one, which was obviously the weakest in the chain, showing a
reversed
voltage.
You have demolished our own argument. All cells were treated identically,
yet one has collapsed! You can't use that evidence to support a claim that
cells treated differently are more liable to collapse (which I assume is
what you are trying to say).

Collapse of one cell is the most common mode of failure for wet cell
batteries, but it is not associated with differential discharge rates.

For years battery manuafacturers have provided a 12v tap across the first
eight cells of high voltage industrial batteries. There has never been any
evidence that using the tap shortens the battery life, and it has never been
the experience of the users.