Disco Tdi Charging System

[jddisco200tdi]

The battery light on the dash is just showing up. Its a bit brighter at idle.
What does this mean ? Is the alternator not charging properly or are the batteries about to crap themselves.

Some info. The alternator is original, 14 years old marelli 65 amp. It bearings are noisy, but they have been like that for 50k (5 years).
The batteries are 6 & 7 years old but still measure 12.6 volts. (they are connected in parallel).

Are there some tests I can do to determine whats at fault ??

Thanks for your help.

[ladas]

This is normally a sign that the ALT is not putting out - it could be the unit at fault, or poor / dirty connections -

To test the ALT connect a low range voltmeter between ALT terminal marker B+ and the poss terminal of the battery - switch on the headlamps, start engine, run engine at 3,000 rpm note reading on meter.

Transfer the meter probe to the frame of the ALT and the NEG terminal of battery - note meter reading

If reading exceeds 0.5 v on poss side or 0.25v on the neg side there is a high resistance in the charging circuit