I’ve got a dozen that I swap between lights and battery boxes so they’re still a thing here. A 2S2P box with 4 x 3500mah cells will run an IW-XE and Secula rear light for about 7 hours.
I also replaced the dead 2,000 mah battery in a mate’s expensive,’sealed’ front light with a new 3,500 mah model when the original failed.
I think it’s worth being careful about charging them. I do worry a bit about the sealed packs and how effective the balancing is, but charging them in a dedicated charger achieves good balance every time.