With my 17.5W, the Samsung 50S should be perfect.I got them in NZ and yes, tested and approved by our genius Mooch. They are Samsung 50S 20a 21700s. I'm at 10A with my 30 watts, so they are at the top of his recommended list. I think for 15A/45 watts and higher he puts the molicel P45B first.
Mooch's Recommended Batteries
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They are difficult to obtain here in Norway, Molicel 45B are easy to get.