Hi,
the battery of my sport 750 doesn't work any more ; so i've looked around, and
an lion ion is about 395 (!!) euro's and weights 1.2 kg (!!!!!!) with the high place it has, weight is important
an gel battery is 86 euro and weights 4.5 kgrs
and care free is 101 euro and weights 7 kgrs
and an 'normal' battery 75 euro and 5 kgrs,
any one has an gel and is he ok with ? that seems the reasonable solution for me : no leakage and resonable price
plus i've read that some people mount an modern voltage regulator,does that make any sense ?

I have had pretty good luck with the Oddessey gel batteries. Lasts over 5 years with a trickle charge. Regular batteries are generally good for 2 seasons or so, but work fine for their duration.
Can't comment on LiOn batteries with the older system.

phil