electrical problem, valmet/valtra

[summo]

The battery warning light on my Valmet 6200 has come on faintly, getting brighter when I rev the tractor.

The battery is nearly new and has 12.5v when isolated, once running it has 13.6v across the terminals. The alternator shows 14.6v (if I recording it across the right terminals. I've tightened the belt etc. check all connections.

The battery earth seems ok, as if I volt check between the + terminal and chassis I get over 12v too.

I'm at a loss? Anybody had a similar issue?

Thanks in advance

 

[DieselMonk]

Check for belt slippage and if that is not it, I'd check the diodes on the alternator. All the plates in the battery are covered with electrolyte and not sulphated to the go no more? check this with a battery load tester.

 

[summo]

yeah battery topped up and fine, belt was fine too, but tightened it bit more.
Diodes, can they be replaced or are alternators more like a sealed unit these days? Thanks