Extracting 25W from a pair of 18650 li-ion in series
Suggested discharge rates are usually 1C - one full discharge per hour. This equates to, for example for a 1500 mAh cell, 1.5 A discharge rate. There are specialized cells that can go much higher C discharge rate - RC car and helicopter cells can be rated 50C or more. There are also lower discharge rate cells that can be rated as longer life, higher temperature ranges, etc.

I haven't seen a 4100mAh 18650 cell, so it's unlikely your cell could handle that rate of discharge safely.