Dimm battery light????

[Rusty_CallyT]

if it gets brighter as revs increase its the reg pack on the alt and will need replacing before it does any damage

[MickM]

It's a shame that there are not two lights; one to show when the batt voltage was higher than the alternator and one to show when the alt voltage was higher than the battery. That would give you more of a clue. If you've got a multimeter you can check it yourself though...