I assume your going to put this in your bike
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There are many models to chose from, the only thing I would recommend is stay with a lead acid battery.
I work with DC power plants and deal with battery's as small a 6 Volt sealed cells to lead acid battery's that weight 600 Lbs. (272 Kg).
I know gel cells/sealed battery's are very popular, how ever I do know that you will get a longer life from a good quality lead acid battery.
Sticks
