On Tue, 27 Apr 2021 05:12:15 +0100, Harry Bloomfield, Esq.
wrote:

snip

I don't make such use of my car, so it sits in my garage whilst unused
and I have it plugged into a charger. The charger comes on for 20
minute each day, timed by a Smart Plug, just to keep it near a full
charge.

I'm not sure that's the best plan, especially if it's a reasonable
current / smart charger.

Like many battery chemistries, lead acid batteries don't like being
stored at full charge (the acid is at it's strongest and so most
corrosive) and if the battery isn't losing much charge between
charges, you may be constantly 'topping off' the charge, again, not a
good idea.

So, if the battery can still easily start the car after being idle for
say 4 weeks, maybe either:

Leave the charger (if 'smart') on 24/7. 'It' will get the battery to
full charge and then just sit in 'maintenance mode', monitoring the
voltage and only applying a small charge current in pulses when
required.

or

If not a smart charger, only have it come on for say 1 day in 10,
giving it a chance to fully charge the battery but not keep doing so
daily.

The bottom line, you really only want to protect the battery from
going flat (damaging the battery) but whilst being able to start the
car when required, even at short notice.

When you dis/re-connect a smart charger it *may* go though a full
charging cycle, including some time on the bulk phase.

I am about to make an 8 way charger multiplexor (managed by my home
automation system) that allows me to switch a relatively expensive
smart charger between up to 8 LA batteries, once a month, spending a
day on each.

Cheers, T i m