So I've been doing some research on these LiFePO batteries. I talked with a FAA electrical Designated Engineering Representative. He points out that although the LiFePO batteries are safer than other Li chemistries, when they fail they still put out electrolyte that is about as flammable as gasoline; whereas other Li chemistries put out gas that ignites immediately when in contact with oxygen.
Yes, this is completely contrary to what wikipedia says about LiFePO.
Check out this guy's experience.
As a mitigation you could put the battery in a stainless steel box in the same way you put a stainless firewall between you and the engine. With this setup you have to make sure that the box is well ventilated with a 1.5 inch DIA tube to the exterior recommended. The failure mode can be explosive so the fire isn't contained it can cause shrapnel on top of the fire hence the large vent recommendation.
The DER also points out that even tiny cell phone batteries have a fire ball 2-3 feet in diameter when they fail, you can imagine the fire ball with a battery like we're talking about here. Also people point out the low failure rate of cell phone and laptop batteries but they are in relatively low charge and discharge situation unlike cranking an engine which makes them more susceptible to failure.
So it may make more sense to use these batteries for backup batteries rather than cranking batteries. I run 2 PC625s, one for cranking and one for emergency backup so I could still save 10 lbs.
I'd like to see someone take a Shorai battery and make it fail to see what the failure mode looks like. How long does it burn, how hot does it get, then a box could be designed to contain the potential fire.
Keep all this in mind as you experiment with these batteries, everybody wants to save 20 lbs and this sounds really promising but I don't want to see anyone get hurt.
Bill
N84WJ, RV-8, 700 hrs
http://rv-8.blogspot.com/