Battery dead - My fault?

[babs]

I bought my Mk4 Polo 3 months ago (M Reg, 40k miles) and it's been fine so far, but this morning when I came to turn it over for work - nothing. It tried the first time, but then nothing. The clock has reset, and I got in to work with a rolling bump start (it didn't die when I put the clutch in so I assume the alternator is fine).

The only changes I've made is installing a JVC headunit (ta trem) - still using the stock speakers. The only reason why I wondered if it might be my fault is because of the way I wired it. I only had a few wires available on the wiring blocks, and I notice that I can turn the headunit on when there's no key in the ignition. If I leave the fascia on the power light stays illuminated when I lock up, so I assume it's wired to 'always live' (or whatever it's called, I'm not the most technical with this stuff).

Could the battery being drained be my fault because of the way the headunit is wired, or is it just an old battery? My father-in-law who gave me the push this morning thought it may need the water in the battery topping up. I've noticed that it's never 'instantly' turned over as long as I've had it, it's always needed a second or two and occasionally there's a slight 'whirr' noise after it turns over (similar to the noise if you keep the key turned after the engine is already running). I just put that down to the starter or something

 

[Jupitus]

I'd be in the 'old battery' camp, tbh.

 

[DaGaffer]

Could the battery being drained be my fault because of the way the headunit is wired, or is it just an old battery? My father-in-law who gave me the push this morning thought it may need the water in the battery topping up. I've noticed that it's never 'instantly' turned over as long as I've had it, it's always needed a second or two and occasionally there's a slight 'whirr' noise after it turns over (similar to the noise if you keep the key turned after the engine is already running). I just put that down to the starter or something

I think you need to get your alternator checked. That whirring sound is a sign of a duff 'un, which would be why your battery isn't charging.

 

[Jupitus]

The whirring could well be the starter motor spinning up but without enough 'oomph' from the battery to spin the arms out fully....

 

[babs]

It happens after the car starts, after it's actually running. Just for half a second after it actually turns over.