The Sun Tachometer transmitters that I have in My 1971 37'Egg harbor boat have a sticker on the transmitter claimin that they require a 1.35 volt mercury battery which appears to be the approximate size of a AA battery.The sun part no. is 1766-7.My transmitter model no is EB-9A.Maybe this is helpful to you .ixpacman(a)aol.com