In article ,
"Meindert Sprang" wrote:

That is exactly what I meant and exactly the reason why it can go wrong. So
I would like to invite you to shoot holes in my following argument:

The charge of a battery is the product of current x time.

Both batteries are in series and one load is connected to the set, operating
at 24V. Another load is connected across only one battery, operating at 12V.
So it is evident that one battery is discharged more than the other.

I start to charge the set in series, so the current through both batteries
is exactly the same. Since one battery is discharged more than the other and
the current throug both is the same, one battery must be charged longer that
the other. Exactly how am I going to achive that with the same current
through both batteries?
One battery will reach the full state before the other but is still being
charged with full current because the other battery hasn't reached the
voltage that corresponds with full charge.

Now, if you can come up with an valid argument why this shouldn't damage one
battery, I bow and take my hat off.

Meindert

One thing you left out, Meindert, is the fact that the 12Vdc load is
still there, and consuming part of the charging current across that
battery, which only makes the problem worse.....

bruce in alaska
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add a 2 before @