I have a similar situation to the OP.
I have 5 Shelly TRVs. On four of them, the battery is draining very slowly, but the fifth one is draining much, much faster (see attached image). [ Edit - look at the right hand section of the graph only from around January 2024 - the previous battery data was for the Eurotronic TRVs that the Shellys replaced ]
The TRV in question probably moves the valve less frequently than the others too, as it is on a small radiator and tends to be 100% open more often than the others. It does probably have the weakest Wi-Fi signal in the house, though.
I was wondering if the OP had solved their issue?
Thanks!