A 20A battery will work great. I like the Samsung 25R's which I have bought from RTD Vapor.
1. AW 1600mah 24A
2. Orbtronic SX22 2000mah 22A
3. LG HE2/HE4 2500mah 20A
4. Samsung 25R 2500mah 20A
5. AW 2200mah 20A (new)
Only buy batteries from a reputable supplier (not ebay or Amazon) as there are many counterfeit batteries being sold. Here are several reputable battery suppliers in the US.
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RTD Vapor
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Illumination Supply
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Lighthound
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Orbtronics