A few years ago I was using my Speedlight daily. I initially used Energizers or Duracells, and the chargers which came bundled with them. On the whole, I found those options unsatisfactory. I switched to the Amazon basics NiMH batteries (made in Japan). They were a significant improvement. More importantly, I acquired an Opus BT-C2400 charger. With its Discharge/Refresh option, I have been able to salvage batteries which went unused for too long (I no longer use the flash daily). I was even able to rehabilitate a set of Energizers I had thought useless. It can take 12 hours plus to accomplish this, but it is worth it. All that said, I recently purchased some AAA Amazon batteries (made in Malaysia). On arrival, only four of the eight were fully charged. and, initially, I wasn't able to charge the others. Amazon sent a second package, and the same was true. Half were not fully charged. Eventually, by repeatedly discharging and recharging, I was able to salvage them. I have a suspicion that a charger with the Discharge/Refresh feature is more important than your choice of battery. All the brands others have mentioned come with excellent reputations.