I picked up a LiFePO4 battery at Oshkosh from earthX, model ETX680. I Installed it at the show and now have a bit of time with it for evaluation.
It is amazingly lightweight... 4.12 pounds on my scale! This replaces my 14.4 pound PC680 AGM battery. A real savings of more than 10 pounds. Crazy.
The form factor is very close to the PC680 and the idea is to use the existing battery box. This works with a couple of notes. The earthX battery is about an inch narrower and just a smidgen thicker and when first installed I had to rock it back and forth in the box to get it in and could not get it to seat all the way to the bottom. Initially it looked like it might not ever come out!
After flying nearly nine hours home it worked itself into the box and now slides in and out just fine.
The terminals are center mounted so I had to fabricate new hold downs. I made a couple of tabs out of .063 using the existing nut plates. This worked out great.
The battery from right out of the box had a strong charge and delivered around 12.8 volts to the bus. During my departure the alternator was flowing around 25 amps to charge, that dropped off gradually and after 40 minutes or so it was fully charged. Pulled from the plane with a full charge my meter shows 13.7 volts.
The chemistry for this battery is quite a bit different than a traditinoal lead acid. The battery will not fade voltage as it discharges or comes under heavy load. It will hold and deliver close to the rated voltage until it nears the end of its capacity. Very different... even cranking the starter the voltage on the bus was above 12!
Apparently, any lithium based chemistry is based on 3.3 volts per cell and there are 4 to make up a 12volt pack; actually 13.2. It is critical that these individual cells be managed for charging. EarthX uses redundant built in charge management circuits within the outer case and includes a remote status indicator and contact. The indicator or the case faces the firewall and I have not yet connected the contact to my panel.
There has been quite a bit of discussion about the safety of Lithium batteries in general... the advantage of the iron phosphate derivative is its thermal and chemical stability.
Fly Low, Go Fast, Turn Left