Upload & Sell: Off
I replaced mine last year with LiFePO4 's
see this link http://www.batterymasters.co.uk/Product-Li12-12,-12v-12Ah-Lithium-Iron-Phosphate,-LiFePO4-Battery,-Charger-Included.-L(mm)-W(mm)-H(mm)-151-98-97.5_2628.aspx
expensive but light... If you have two, then I'd change one with the heavy one at 20 euros and the other with the expensive one.
One thing I learnt with mine was that the newer battery (back then) couldn't take a full power pop... I suspect the battery wasn't 'high grade'.
email me if you want more infor.