CR 2016 = 20 mm wide x 1.6 mm deep CR 2025 20 mm wide 2.5 mm deep Etc all should have nominal voltage of 3v if it fits in it could work but may put undue pressure on some part of pcb or even damage tracks so always best to go for right one sounds like you may have a faulty key do you know a radio amateur or anyone who could check key is transmitting ? best of luck