Dave Plowman wrote:

In article ,
The Natural Philosopher wrote:

Lots of things like cars and caravans regularly connect the batteries in
parallel. They charge just fine. They even discharge just fine, but its
obviously advantaegous in e,g. a camper to discnnect teh primary engine
battery from teh camper to ensure you can start the engine the next day
if you flatten the lesiure cells.


There are diodes available that do this automagically...


There are relays that do it 10000% better automgically. Diodes DON'T
work BTW. You need full volts on charge, not full volts -0.6v or whatever.