they basically just put a usb charger port on the protection board. You can get them from a slew of other manufacturers as well. Not something I'm a huge fan of though.
Example
Protected Vapcell P1835A 18650 10A Button Top 3500mah USB Battery - Genuine
I'm a big fan of USB powered stuff for the reasons that Go Sidemount talks about with travel, but I'd rather take a charger, especially since I'm almost always charging multiple batteries.
For freshwater cave diving I don't think it would bother me as much but really don't like the idea for saltwater dives. Unless I'm missing something though, you can just charge the batteries in chargers (my preferred method to as well) like normal, since it takes a 18650 battery.