Low discharge NIMH. Eneloop pioneered this and are very good. I use them for everything. For flash there are very expensive eneloop pros. I have some Amazon basics high capacity that work very well. The high capacity is like eneloop pros.
The eneloop pros and Amazon high capacity recharge the flash faster but discharge faster in a drawer and have only 200-300 or so charges in their life vs 1000 for standard envelops.