I got stranded at the weekend with a flat battery -- I'd left my sidelights on. The mechanic that attended tested the charging voltage under idle and load & reckoned charging/alternator was fine. He didn't seem to think the battery was faulty, but didn't do a drop test.

The car is a UK Focus 2.0i ESP from 2000 (mk.1)

I currently have a Moura Intelligent 063+ battery fitted rated at 45/400. It was fitted 1 Dec 2009 with a 5yr warranty

I'm wondering what capacity I should expect

- ambient temp around 5-12 deg.C

- Typical day is

a) 5 miles country roads (to gym), 1 set of lights 30-60 mph < 15 mins

b) 5 miles country roads (to work), 30-60 mph normally 1 set, recently 3+ due to roadworks (*) ~ 15 mins

c) 4 miles (home), o****ry roads ~30mph ~ 10-12 mins

On (*) above the roadworks are currently resulting in a slow 4 way controlled junction leading to an up to 4-5 minutes wait. I've probably switched the engine off, probably once, at this junction to save fuel/emissions

I don't do many longer journeys - sometimes at weekend, but probably nothing for last few weeks. One reason why I rather fancy a Focus EV (or leaf) ...

During the week I had left the interior light on overnight on one occasion (8-10 hours)

On Saturday I repeated a) to get to the gym but accidentally left lights on (they switch to sidelights automatically with ign off).

The car was left like this for approx 2.5 hours

On return clicking only - no start

After jump starting, running for 5 mins, and driving home in lower gear/higher revs, I put the battery on to charge after a) in reverse, but my (smart) charger reckoned it was fully charged within 10 minutes (??)

The following day I started the car 8 times over a couple of hours, and left sidelights+interior light on for about 4 hours - result=dead battery

I've charged again, started once this morning, plan to leave lights on for the day and see if it charges again.

The battery is not tested yet, but is only 2 years old. I'm struggling to find the paperwork for the warranty, and slightly more complicatedly the location selling the battery has closed, though the same "group" still runs other outlets, but didn't sell the same parts. I can probably get sorted if faulty but may take time.

Am I expecting too much of the capacity? Is the bottom line this is normal, I screwed up with hitting the battery too hard this week? Or is there an indication there could be a fault? I may take it to the local battery shop for a test... Is the correct fix simply to have the user reprogrammed to not be stupid enough to leave lights on? (and/or get a higher capacity battery for safety). Am somewhat tempted to get a "starter" unit for backup.

How many starts would you expect the battery to manage?

How much power does leaving interior light on take (I'd assume it's around 5W so even overnight inconsequential?)

How about sidelights ? Around 48W/4A? -> so just this could be 1/4 capacity?

Checking battery sellers some more perhaps suggests 60-70 Ah as higher end (maybe better for lots of short journeys) so is it fair conclusion here of user error (in purchase, & in usage)