Had been having classic "battery is broken" issues.

Bought a new battery & everything seemed ok, alternator checked with multimeter & definitely sending plenty of current into the battery when running.

Had fallen into the habit when persevering with old battery, of always plugging in solar panel charger when not in use. Continued with this habit after changing to new battery. Went on for ages with no prob.

Couple of weeks ago 3 lads broke in and stole the solar charger. Thought, no worries, battery is new, it'll be okay anyway.

But no! left vehicle for one day with ignition off, and battery flat.

I'm planning on getting the multimeter out again & checking the battery drain whilst pulling fuses one by one to try and identify the problem circuit, but does anyone have any suggestions regarding common problems that lead to this?

Just to throw a wild card into the mix, this is a 1986 RR classic that's been chopped about severely to turn it into a fairly rough basic off-roader. There's chopped-off loom ends everywhere in sight :-(

Beyond the multimeter it's educated guesswork I think

 

Just insulate each wire end in each loom to be on the safe side.
......

 

Insulated everything bare I could find, tried to find a more significant leak than the 8mA I'm putting down to the clock, but no luck pinning down a definite cause.

So took battery out & played about a bit on the bench with it. It seems as if it's maybe become lazy somehow. Wouldn't take a significant charge for ages until I rapidly charged & discharged it afew times, high current charger, & then virtually shorting it out with an old lorry starter motor

Came back to life after doing that for a bit & now everything seems fine, plenty of charge coming in from the alternator, seems to hold a charge for a good time, cranks okay etc.

Sulphation? Wouldn't have believed it but then again vehicle is often used for very short runs only so maybe the charge in it has slowly been dropping day by day & not getting replenished enough