SRAM’s ETAP shifting components have individual batteries on the derailleurs unlike Shimano’s Di2. The batteries are swappable should you lose power or if you have a backup battery.
A nice design touch is on the battery cover. It has a little molded in indicator that you can set to remind you if it’s an empty or full one. A design detail that they could have omitted but didn’t.
Nice one SRAM. Thoughtful design.