We have a lot of batteries. The kids’ toys seem to use endless quantities of AA and AAA batteries plus many of my HomeKit smart devices including sensors and radiator valves are battery powered (typically AA or 1/2 AA). Over the last few years I’ve been replacing disposable batteries with rechargeable batteries to reduce waste. So far every device has worked successfully on rechargeable batteries (even when the manufacturer didn’t recommend them) although in some cases low battery warnings are triggered almost continuously since the Nickel Metal Hybrid (Ni-MH) rechargeable batteries are slightly lower voltage than regular disposable alkaline batteries (1.2 versus 1.5 Volts).
Last year I came across a Lithium AA battery that had potential to avoid such issues. Normally Lithium cells have voltages in the 3-4 Volts range, but these batteries have internal voltage regulation to reduce this down to 1.5 Volts. They need a special charger, but have the potential to eliminate the almost continuous low voltage messages.
I’ve now been using the first of these for six months. They have indeed eliminated the low battery messages. I still recharge the batteries at the end of every quarter regardless of whether I have a low battery warning or not. For the Ni-MH batteries they get replaced because the low battery warning is on most of the time anyway, while for the Lithiums I’m anticipating that the voltage may dramatically collapse not leaving time to change them after the low voltage warning is triggered. I now have three sets of eight which is enough for all my Eve Thermo smart radiator valves (eTRVs).
They are currently available via both Amazon and eBay, although Amazon seems to have the better prices whenever I’ve looked.
My sole criticism of these batteries is that they only seem to be available in sets with a charger, and not as just cells, so I now have three chargers.
I now have rechargeable Lithium cells for all my Eve Thermos (2 x 1.5V AA each) and Eve Door and Window sensors (1 x 3.7V 1/2 AA each). The Eve Room and Eve Motion sensors don’t seem to mind the lower voltage Ni-MH cells.
I have subsequently had one radiator valve that showed a low battery warning unexpectedly quickly, but I think that this was a poor contact. The EBL batteries aren’t absolutely the same size of the prior Ni-MH cells and I suspect we’re making poor contact. Addition of a small washer on top of the terminal seems to have turned a reported “low battery” into a healthy one without recharging.