How Do I Diagnose My Battery?

[Pete81]

I was running a few errands early today (only over 3 miles or so) and went to pick up a friend. As I was sitting outside hers waiting; I pushed the right-hand lever/stem/stalk/whatever it's called down to do a manual wipe of the windscreen... at which point the clock reset to 1:00 and the radio went off. (Engine was already off. Heating was on due to foggy windows.)

I tried to start the engine but no luck. (Didn't even turn over.)

I called a friend and he suggested the battery. I told him the radio still worked and dashlights, wouldn't they be off if the battery was the problem? He wasn't sure either.
So he came and picked us up (we were going to attempt a push-start but it was very dark, on a busy road and there was a hill!) and we just left the car for a while.
I went back on my own 4 hours later and the car started up. I switched the engine off, waited a minute and tried again... started again.

I drove the car home and now I'm wondering what to do.
Are there any tests I can self-perform to narrow down the problem?
When checking the dashboard lights, what position should the key be in? Or should the engine be running?

Thanks for the words of wisdom.

[Pete81]

Small update/additional details: (Can't edit posts yet.)
My experience posted above, happened in pretty heavy rain.
About an hour before the problems, I'd added £10 or so worth of petrol.
These may not be related to the problem but I figured they'd be worth a mention, on the off-chance etc.

[VTR_Craig]

unless the battery is completely flat, the dash lights will come on when you turn the key.

because you went back to it later and it started fine, the battery sounds ok. You mentioned heavy rain, possibly getting into electrics? maybe a connection on the battery terminal?

Have a look at the contacts on the battery and then make sure the fuse box is not full of water.

[Pete81]

Originally Posted by VTR_Craig

because you went back to it later and it started fine, the battery sounds ok. You mentioned heavy rain, possibly getting into electrics? maybe a connection on the battery terminal?

Interesting, could this be done via a leak where the the aerial is joined to the car roof?
Every now and then (after heavy rain) my interior light is filled with water and the light itself has never worked since I got the car (almost 4 years ago).
I pry the light off with a flathead screwdriver and dump the water out.

I've got some sealant around here somewhere and been meaning to attempt a seal around the aerial to stop the water getting in.

Possibly related?

Thanks again.

[Pete81]

(Still can't edit, not enough posts, but here's more info.)
I spoke to a friend in work today who reckons that; because I always drive the car to do little local runs (1-3 miles) I'm not charging the battery properly and that I need to run it up a motorway at 30mph+ for a while.
I used the car twice today with no issues, no maybe not the battery?
I was going to use sealant where the aerial connects to the roof but it's been raining all day, waiting for it to be a bit drier.

[Manu]

You had a short somewhere because of moisture, I can't really see beyond that. To test the battery, use a multimeter. I'm guessing you have a 40 amps, anything below 20 is not too good.