Unfortunately, the pale blue documentation does not mention this. But these are lithium batteries. For your information, here is the manufacturer's contact address: contact@paleblue.fr

Coast Zithion-X 1.5V AA performes well in series with the Optimized Voltage technology you get expected behavior because they are 100% compatible with any device that works on regular alkaline batteries. They work in flashlights where many constant voltage products fail and the battery indicator also works unlike in constant voltage products that due to their design “hide” their charge state.

You can find the Coast Zithion-X AA 1.5V USB-C rechargeable batteries here: Coast AA USB-C (4 pcs., AA, 2400 mAh)