apparently the specific type of battery. eg Panasonic eneloop 1900mAh is important. Perhaps tado help are confusing the issue, and it's really about SIZE not TYPE, and its other issues that are causing battery failure. Perhaps it's both. But they need to be clear. My understanding regarding other brands and capacities is that there is a question mark over physical fit. That would include the 2500 LADDAs, just like the larger Eneloops. Welcome to the brand new Panasonic Eneloop AA rechargeable batteries with improvements in performance and sustainabiltiy. These new Panasonic Eneloop rechargeable AA batteries hold even more energy and have an improved capacity of 2000mAh. This new version has up to 7% more capacity and will perform outstandingly well in demanding situations.

Also, thinking this hypothesis out loud - What if VERY cheap non-standard battery types tend to heat up (event) at mechanically idle current and thus cause reading error? (I don't think anybody will do that though :) ) So in essence seems to me there are 3 design issues with the radiator thermostat in connection with battery use that I have discovered. Pretty major I think and im mulling getting rid of them Many customers will have known and used batteries under the Sanyo brand name. Panasonic Eneloop Pro AA batteries are the ideal choice for powering high drain devices such as digital cameras, flashguns or photo strobe flash lights. The Panasonic Eneloop Pro AA batteries provide more than twice the number of flashes per recharge in less than half the time, compared to conventional alkaline batteries. The batteries are also perfect for wireless keyboards, wireless mice, game controllers, radio controlled toys and a range of everyday electronics. These new Panasonic Eneloop AA batteries can be recharged up to 2100 times. These revolutionary low self discharge rechargeable batteries retain 70% of their charge for up to 10 years. The Panasonic Eneloop AA rechargeable batteries are pre-charged using solar energy.I think this is why Tado doesn't recommend other types of batteries. By observing their "very diligent" documentation style I can imagine that they don't want to recommend inserting fingers or tweezers into the battery compartment in case things go wrong. The very latest 5th Generation of Panasonic Eneloop Pro AA 2500mAh Rechargeable Batteries for professional use are AA size NiMH 1.2V rechargeable batteries. Many customers and professional users will have bought and used this product under the Sanyo brand name. They're on the charger now, so far too early to comment on performance in the long term, but I tried two pairs in one of my Tado SRTs and the fit was easy peasy. Also, no problem to operate the SRT with the "ready to use" charge they came with.

https://community.tado.com/en-gb/discussion/3099/released-rechargeable-batteries-in-smart-radiator-thermostats-va02-hardware-revision