Hi, being into electric powered radio controlled aeroplanes, I can tell you that the lithium chemistry is not one of longevity, you're much better off with lead acid, and as was suggested you need a different charger, not to mention checking if the charging system on your bike will accommodate it (it's possible that the batteries have circuits on them to prevent overcharging).
Stick with the tried and tested, and if you can, get an optimiser, I've never had a dull moment since I statrted using one, and I'm led to believe they condition the battery too.