The basic gell cell charger is a constant voltage supply. Current limiting is optional.

However, you're not going to get around the fact that lead-acid chemistry gives you about 18 Wh/Lb.   Nicad or NIMH would be a significantly better choice. Nicads are more robust, NIMH packs more watts in a can.

Li-Poly is looking interesting, but still requires careful attention to charge, and discharge cutoffs.

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