dead battery

paul_c said:

What's the fuse box and a couple of relays under the bonnet for?

Did you use a voltmeter and confirm the alternator is charging the battery properly? If so, what are the readings etc?

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paul_c said:

A cheap multimeter will do the job, so long as it can read volts accurately (like, to 1 decimal place but preforably 2 decimal places).

I'd take a whole series of voltmeter readings to establish the general health of the electrical system, for example:

1. Battery voltage before starting
2. Battery voltage just after starting

1. should be 12.6-12.8V (a fully charged battery is 12.8V or so) 2. should be around 13-14V initially, although once the main input into the battery has dropped down, it will settle to low 13s.

Also they're useful for monitoring if a battery gradually loses charge.

Don't forget to allow for "surface charge" of the battery - just after its charged, it will read an artificially high voltage, but once significant current is drawn from the battery without recharge, it will drop to a more meaningful figure.

The battery doesn't need to be fitted to the vehicle but if its not, you can't check the charging system, only the health of the battery. Plenty of battery faults are charging faults which cause the battery to be discharged. Once left in a discharged state, chemical reactions within the battery permanently harm it so it can no longer hold decent charge.

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