Many owners do not realize it has it's own battery that requires regular replacement. If you do not replace the battery at the specified time you are out of compliance and your remote switch will not work without a serviceable battery. (And you will be unable to RESET your ELT remotely should it activate inadvertently.)
The most common type of RCPI uses a battery that resembles a half-length AA, but is actually a SIX VOLT battery. It is a PX28L (Lithium) or PX28A (Alkaline). They can be difficult to find because many mfr's of these type batteries use different designations. You might find it listed as a 2CR-1/3N, or a L544BP, or K28L.
It is most commonly used as a PHOTO battery. I found that the local Radio Shack handles them, but the personnel at the store was unknowlegeable about how to cross-reference the battery.
It is Radio Shack part number 23-266 if you want the Lithium version. I recommend Lithium even though they are twice as expensive (about $10) as the Alkaline because:
1- Lithium has an 8-10 year service life. (ACK specifies that it must be replaced at 8 years.) Alkaline is only 4-5 years.
2-The dang thing is not easy to replace. It requires the removal of 4 tiny screws that thread into 4 tiny (1/4") nylock nuts that are not backed up and will turn when you turn the screw. The nuts are so close to the case that they are very difficult to hold while removing the screws unless you use an "ignition" open-end wrench. This means you have to get to the dang thing. It took me almost an hour (and I had to remove part of my avionics panel) just to change this little battery.
I do not want to do it for at least another 8 years!
Do NOT confuse this battery with the ones that fit in many auto key-lock remotes. It looks similar but it is not. It is a SIX (6) VOLT BATTERY. The POSitive end points AWAY from the front of the unit. (And you're going to need a very small phillips screwdriver to open the case for the replacement.)
Don't forget to make a logbook entry.
