Technical '04 Multiwagon battery/charging - earth fault??

[notmyfiat]

Hi, folks.

I'm helping a mate with his Stilo - jump started earlier today due to flat battery. I'll poke around in threads on here to see if I can answer my own question but I post this in the hope someone can help.

We haven't got going with diagnostics really, and the battery may well be shot, but there was one behaviour I saw today that I want to query.

I had a voltmeter on the battery before, during and after charging. It started as 12.3V, after disconnecting charger it was reading 12.8V, but dropped to 12.5V after a while, so I'm not holding out for the battery lasting. Anyway, the observation was that it started fine, reading 12.3V at idle. I got him to give it revs, read 14.3V (iirc), but... stayed at 14.3V when idling again. I wasn't expecting that.

So - question is... is this expected behaviour of the charging circuitry, or if his battery is goosed and we replace it, what can I do to make sure there's not something going on with alternator/earth that will kill the next one too?

Cheers,
Monkey.

 

[notmyfiat]

I think what confused me was that at first idle, the alternator did not appear to be charging the battery... but after revs and back at idle, it did.

So I'm wondering whether a) this is expected behaviour of the charging circuitry, or b) there might be a poor earth that caused the no-charge-on-first-idle that got "kicked" for the alternator to keep charging at second idle.

Any comments at all?