Lithium batteries in 912iS

The folks that designed the 912iS FWF kit for the Zenith 750 suggest lead acid batteries to avoid charge system overload.

https://youtu.be/TzTieV0EvSY?t=2294

The Van’s RV-12iS uses an EarthX ETX900 in front of the firewall. 

The lithium battery in my original configuration died quite unexpectedly (and inexplicably) on me one day, luckily on the ground.  Recharging this particular battery (not EarthX) from its depleted state did not seem a viable option, and getting a duplicate one (from overseas) was problematic, as it could not be shipped by air!  

I decided to replace it with an Odyssey "Extreme" lead-acid battery, which has given me absolutely no trouble for nearly three years now, including some pretty harsh New York winters.  Yes, it weighs (just a bit) more, but I know I can recharge/replace it very easily.

A couple of comments...

1) Lead acid for system overcharge makes no sense...LFP 12v batteries have a higher voltage tolerance than lead acid (15.2 vs 14.5)

2) With duel alternators and a battery you have triple redundancy that should be enough for anyone.

3) Perhaps the EarthX flow chart was done by their Lawyers not their engineers

4) I have an EarthX works fine, fit the largest you can. IS engine reccomended battery capacity is 16 AH minimum so an EXT 900 would be OK

I don’t think the concern is that the battery can’t accept an overcharge voltage, but rather that a Lithium-ion battery may in certain situations (like with a damaged cell) accept a charging current high enough to overload the alternator.  For this and other reasons, Rotax specifies that a battery management system (BMS) must be used in conjunction with a Lithium-ion battery. This is described in the 912is installation manual section 24-00-00, page 4, and further discussed in service bulletin ASB-912 I-005iS.  A battery with at least 16ah is recommended to provide the final redundancy for the engine electronics and fuel pumps. 

The EarthX EXT Hundred series batteries have an integrated BMS that they claim will, among other things, protect against overcharge by limiting the charging voltage/current. Some manufacturers are providing the EarthX EXT Hundred Series battery with the 912iS engine. I see that Van’s RV-12iS is on that list. My Bristell NG5 912iS came with a 16ah EarthX battery, which was optional and installed by the US distributor.  It has been working perfectly for almost 5 years now.  

https://earthxbatteries.com/earthx-inc-proud-add-vans-aircraft-oems-using-earthx-lithium-battery-new-rotax-912is-equipped-rv-12is