If by any chance, a key is locked up in pressed position, it drains battery. If the TV has a normal LED also which blinks when ever the remote is used, it could indicate.
alternately, you could take your Remote very close to an AM or Shortwave of a radio on lower frequency like 3Mhz or 5MHz, the remote signals can be heard as clicks of noise in the radio.
Now even without pressing any key, sequences of clicks are heard, you can ascertain that one of the keys got stuck
Perhaps you can open clean the rubber pad and put back it should serve.