Ignition backup battery failure on run up - FX3

[Tsquared]

Earlier this summer while performing a engine run up prior to a flight I had the Right Mag emergency backup battery fail.

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Video taken after aborting the flight and returning to the hangar


The PS-1221S battery had been replaced in October of 2025 during my conditional inspection. Normally I fly my FX3 about 120 hrs a year, but I am down to about 50 hrs a year due to work, weather and an elderly mom who has needed a lot of care recently. Prior to this attempted flight on June 6th, the plane had not flown for 3 weeks and had less than 15 hrs since January. Whether this is a factor or not, it’s worth noting. Also note the battery had a date sticker of 06/20/25 and this failure occurred on 06/06/2026.

During the run up the voltage dropped to 5.9 before I shut off the RT IGN Battery. I considered this a failed runup and returned to the hangar for diagnostics.

The solution to this was to replace the PS122S battery with a new one. My new SOP will be to replace that battery one year after the battery manufacturing date and not during the conditional inspection time. I have also changed my engine run up check list to include a 10 sec run on the emergency battery.

if you haven't already changed the alerting on for Alternator/Amp to give you a red and audio alert I strongly recommend doing so. This is aligned with what Cactus Charlie recommended in some earlier threads (see the N40DT accident threads and the ignition battery threads).

I’m posting the videos and pictures as most people have never seen (and hopefully never will) this failure before. Hopefully this thread and the other discussions on the ignition system will educate folks and prevent another N40DT situation where the emergency backup system failed when it was needed the most.

 

[Cactus Charlie]

You are fortunate if you can be shipped a PS 122S that is within 1 year of manufacture date. Read the embossed date stamp. The sticker was likely not put there at manufacture.

Earlier this year I had a battery fail less than 2 months after if was shipped to me. It was over 2 years old and the supplier said their warehouse stock had none newer.

I have data for all my ignition batteries used over the last 6 years and it's obvious to me that elapsed time (since built, since shipped, or since fitted) is not a good predictor of current condition.

 

[Cactus Charlie]

Read the embossed date stamp.

20241218-JA indicates a manufacture date of December 2024.

The battery in my plot above had date code 20240619-JA. The current battery is a warranty replacement with the same date code. It is performing better.