Quote Originally Posted by Eric Page View Post
For those considering EarthX, you might want to look at the electrical section of your engine's installation manual, particularly for electrically dependent models like the Rotax "iS" engines. In the current 912iS manual, the battery specification requires a capacity of "at least 16 Ah."

Looking at the EarthX spec sheet, the ETX-680 and -680C are rated at 12.4 Ah, at a 1C discharge rate. That means you'll only get that capacity from a brand new battery if you discharge it at no more than 12.4 amps. An aged battery, or a battery discharged at a higher rate, will result in lower capacity.

This makes little difference in how it spins the engine starter, but it's very important if both of the alternator/regulator systems fail. That leaves the battery to carry the ECU, fuel pumps, ignition system and airframe buses until you reach a safe landing spot. This is why Rotax specifies a 16 Ah battery, and is one of the drawbacks of lithium chemistries compared to lead-acid in the same dimensional footprint.

If your ship is a day-VFR-only machine, and you don't fly in remote areas or over hostile terrain, then you might be OK with a shorter battery-only endurance. Just be sure that you've done the load analysis so you know your plane's electrical demands and can choose a battery -- and test/maintain it in a way -- that matches your risk tolerance.

As an aside... The Odyssey PC680 is a 16 Ah battery. The EarthX ETX-900 has the same case size as their ETX-680 but offers 15.6 Ah capacity; compared to the -680, it's +$70 and +13 oz. It's still not 16 Ah, but it's darn close. Makes you wonder why EarthX uses the "680" designation for a battery that isn't equivalent to the PC680.
I guess I can say it doesn't matter to me. My plane does not have: efis, efi, transponder of any kind, don't use lights day vfr. so I guess it doesn't matter. But I do go into the back country. When I throw my master switch everything is off to the battery. no memory devices. I have a radio on line and a com (dynon) run a fuel pump (if the mechanical poops) IVO electric prop. outside of that nothing.