My ACK ELT hit the 10 year replace the Duracell CR2 or equivalent Audio Alert battery. I must confess to paying more attention to the ELT test signal on my Yaesu handheld when I do my every 3 month or so ELT Test than I do to the solitary beep the contraption makes after the Yaesu sounds off. As a consequence, I don’t know exactly when failure happened. When I opened the unit, I was surprised to see leakage from the lithium Duracell, with corrosion of the + terminal and spilling over onto a couple of the SMD components. I was able to solder in a copper strip to repair the terminal, but unfortunately, there was so much damage I had to order a new Audio Alert, $42 plus shipping and tax from AC Spruce & $11 for a new CR2. All back to working and not too bad, pricewise.

I have had numerous Duracell alkaline batteries destroy hardware before, so much so that I don’t use those or unknown name brands any longer, but I’ve never had a lithium battery of any sort do that before. Anyway, I switched to a Energizer Ultimate Lithium, and will probably just replace them every 5 years instead of the 10 years listed, and I will promise the airplane to pay more attention to the “beep”. FYI

PS: The main ELT battery is due to be replaced this summer. The least expensive I’ve found is about $275. Those are getting pricey!

Speaking of ACK ELTs: My plane is coming due for it's annual, so I stripped all my "survival" and "camping" gear out, pulled the seats, and all the inspection covers to speed the process.

In this process, I removed the ACK ELT, verified that it alerted properly from a good forward jolt, and re-installed it. I gave it no further thought. The next day, I visited my hangar, and turned on a comm radio for something else, and lo and behold, the ELT was alerting! I got in the back to access the ELT and turned it off, then reset it. Turned on a handheld to verify it wasn't alerting--good to go. Fortunately, I left the handheld on.......

Now, my hangar has an overhead mounted natural gas heater, which blows down right about the middle of the airplane's fuselage, from a distance of ten feet or so. I had sat down for a moment, looking for an AD clearance in my logbooks when the furnace kicked in, and the ELT alerted again.......!!! What the hey???

I turned the ELT off once more, and left it off. By this time, I wasn't sure exactly how long the ELT had been active, so had ordered a new battery. Fortunately, the hangar apparently prevented the ELTs broadcast from getting to RCC. But, now, I was thinking i was about to purchase a new ELT......grrrrr.

Next day, I called ECK tech help (and BTW, if you haven't called them, they are VERY knowledgeable and helpful) and explained to the Tech what had happened, including (laughingly) the fact that the ELT had alerted in sequence with the furnace coming on. His response was "Yep, check and verify that you have a filter installed at the base of your antenna, those come with the ELT kit". I did, no filter. The filter is a small, metal tube shaped piece about an inch and a half in length that attaches to the base of the antenna, inside the fuselage. I ordered one from Spruce, and called Tech Support back. He explained that when the ACK units first shipped, they had lots of complaints of inadvertent and unexplained alerts. Until they finally realized that these were often associated with some outside stimulus....like a fan blowing on the external antenna, setting up a potential on the antenna. Since then, all these units have been shipped with a filter as part of the kit, and the instructions clearly state to install the filter.

I moseyed over to the maintenance outfit, wherein was parked a 172, with, it turns out, an ACK ELT. I explained to the mechanics what I'd learned from ACK. They looked at the 172 antenna, no filter. They then went in their stock room, and found an ACK box. No ELT, but therein was a filter.....not installed with that ELT. Oops. They took that filter over to the plane it belonged to that day.

Long story, but I would never have believed it myself if I hadn't been the one to learn the hard way. Fortunately, my battery would have been due this winter anyway, but.....

Gotta get a filter - check!