I am quite aware of the broad use of lithiums. The hazard imposed,
however, is a function of the size of the battery and the mass of
lithium. A shorted SLA will blow a fuse (if there is a fuse), but it
won't catch fire. If a lithium battery catches fire it will burn until
the lithium is consumed. That may be ok for a PDA or flashlight, but
not a main battery in an aircraft, IMO. The issue is with the lithium
itself; no lithium battery design will eliminate that. Your battery
will likely be constructed from many individual cells. The failure of a
single cell will start the whole pack on fire. Fires on board aircraft
are rare in general, but when the occur they are very serious
situations.

BTW the successful use of a totally different product than the one you
are contemplating DOES NOT constitute a safety analysis. But the tone
of your reply suggests that I am wasting my time here.

Tom