There's a flurry of battery holders that accept 21700 cells, but the power delivery is just too weak IMHO.
From memory, the max output was about 20~30W for the bigger models [0]. For 2 cell types it gives 10W, so barely good enough to slowly charge a smartphone.
From memory, the max output was about 20~30W for the bigger models [0]. For 2 cell types it gives 10W, so barely good enough to slowly charge a smartphone.
https://www.amazon.co.jp/PLCPDM/dp/B0DFPKXQZ1