busa charging

[tex]

ok a question for the educated amongst us - that puts me out cos i'm asking...

ok - megabusa - battery charging voltages

engine running tickover across the battery im getting 13.7 / 8v
turn on lights - bout 9-10v + if i rev the engine a bit and hold it - 12.07v
turn on twin rear fogs - bout 9-10v + if i rev the engine a bit and hold it - 12.07v ish

is that normal??

im guessing that 13.7v is telling me its charging ok but should i see the same voltage with lights on?

reason im asking i left the battery charger off the car last winter for 3 months while the car stood idle - doh - since then its had a couple of go flat moments and its died - it could be the battery is damaged and bringing it down a bit or is it more likely that its simply not charging correctly?

if its not charging hows it fixable? obviously its a bike engine so it hasnt the normal alternator