Most everyone has heard about the newly approved EarthX battery STC for the Cirrus fleet. I’ve been following the project for quite a while and was excited when my installation kit finally arrived. A friend and customer even 3D-printed a test-fit EarthX battery for me a couple of years ago, which gave me plenty of time to think about mounting options. It just seemed right that a new battery should have a properly fitting mount.
The EarthX battery is dramatically smaller than the original battery it replaces. As I looked at the installation, it seemed inefficient to mount a compact battery in a tray designed for something much larger. Naturally, I spent far too much time thinking about how to build a better battery mount.
The old and the new side by side for comparison. You’ll just have to imagine the difference in the weights
My first thought was to fabricate a completely new tray. The problem is that a purpose- designed replacement part starts looking a lot like a design change to the aircraft, which can bring engineering data and approval requirements into the picture. After considering several options, I decided the cleaner path was to modify the existing mount rather than replace it entirely.
Before cutting up a perfectly good battery tray, I needed to determine where the modification fit from a regulatory standpoint. In Title 14 CFR Part 43, Appendix A, paragraph (a)(1) identifies alterations that qualify as Major Alterations. Conveniently, battery boxes and battery mounts aren’t on the list. That means modifying the existing battery mount can be treated as a minor alteration and documented with a standard
maintenance record entry in accordance with CFR 43.9.
My measurements showed that I could shorten the tray by just over two inches while retaining the original width. The width needed to remain unchanged to accommodate the hold-down bracket supplied with the EarthX installation kit. Narrowing the tray would have required redesigning the hold down arrangement, adding complexity for very little gain.
Original battery tray just before liberating it from the airplane
All chopped up with the two sacrificed sections laying in the middle
Structurally, the modified tray looks almost identical to the original, just shorter. It uses the same material, mounts to the firewall using the original four attachment bolts, and requires no changes to the firewall or mounting hardware. Since the EarthX battery weighs less than one-third of the original battery, the loads imposed on the tray, hardware, and firewall are substantially reduced.
Back together with the two sacrificed sections in the middle showing how much was removed
The practical benefit is modest but real. The battery itself saves approximately 22 pounds. My resized battery tray contributes another 1.4 ounces of weight savings (not much, but we use every little bit to justify our geeky decisions). More importantly, shortening the tray creates an additional 2⅛ inches of clearance between the battery tray and the engine, making maintenance access behind the right side of the engine much easier.
New battery in its new digs just about to be secured in place
Was the original access a problem? Honestly, no. Would anyone have complained about leaving the stock tray in place? Probably not. So why spend seven hours cutting apart and rewelding a perfectly good battery mount? Because I can, and because it looks cool.
Now my next challenge is convincing EarthX to pursue an STC to replace our BAT2 with one of their batteries.
© 2026 Paul New
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