On Monday, January 4, 2016 at 1:39:04 PM UTC-8, Chris wrote:
Its time again to change batteries in my motorglider. There are 4 lead batteries with modified (vibration proof) terminals. A major pita.
I have been enviously following the threads for improved batteries for pure gliders. Lighter, more performance, holding their charge, longer life cycle yada yada...
I have more avionics than ever and want more capacity for improved safety but have no room to spare. I would also like to shed some of the weight and get better life. I am ready.
The question is however, how LIFEPO4 batteries will do with a mixed high amp crank demand of a self starter and deep cycle mode during long flights with enough umph to start at the end of the day when needed.
Does anybody have experience or words of (scientific - not regulatory) wisdom?

Not a DG, but I have been using an LiFeP04 for the engine start battery in my ASH26E for a year now. While the engine start battery can power the avionics, I have a separate (LiFePo4) battery for that. You need to find a Li battery that fits in the same spot, has charge/discharge/current protections built in, and has a max discharge capacity sufficient to crank the starter reliably. I measured the ASH starter at 150 amps stall current and 100 or so while cranking. The battery I am using is a CTC LFP128198, rated at 19.8 AH and 160 amps discharge for 30 seconds.

Beware of LFP batteries advertised for motorcycle or auto start which will say something like "20 AH equivalent" as these generally will deliver the same high discharge current for a short time, but do not actually have the AH capacity to run instruments.

I have had no problem at all with the battery, and it cranks the engine much better than the LA battery that it replaced, holding the voltage about 3 volts higher during cranking.