Thanks for that as I had lost my instruction book and I never thought to look on line. Mind you I still don’t know how long roughly they last as when tugging down to Spain I don’t want to have to pull over and change batteries. Last winter I changed them anyway so perhaps I had better do the same again.
The manual says 'up to two years' ...it's at the bottom under 'specifications'.
It does also say elsewhere that the sensors go into sleep mode when the vehicle is not in use, so I would guess that actual life is dependent on vehicle usage.
We've got a TP99 and have just had to change the batteries on the sensors after about 6 years (well, one died so we pushed the boat out and replaced all 4). We don't do that many miles though, 5K a year tops.