"Meindert Sprang" wrote in message ...

No, because the other one is connected in series, not in parallel. So one
battery gets drained faster that the other and that is the success-formula
for wrecking that battery.

No worse, surely, than it would be if there was only that battery and
a 12V system. It has no way of knowing that some of its output is
being boosted by another 12V.

I wouldn't have expected there to be any problem at all with the OP's
idea - but if he was worried, he could always swap the batteries every
season so they get roughly equal use as the 12V supply.

Ian