Following on from the thread about second use for old electric car
batteries: surely as end of life is reached for any cell the self
discharge increases and thus a higher proportion of the charge gets
expressed as heat?

I need to provide hot washing water in one of our vans, about 10
litres is enough and these basin units are readily available for £250.

I can see a split charge system will only charge the second battery
when the main vehicle battery exceeds 13.5V, and even a facility I'm
told that will only charge it on overrun. This will get the water hot
on the run to work.

During the day how does one prevent the auxiliary battery discharging
below 50% DOD, is it by voltage sensing or do VA have to be
integrated?

AJH