You did indeed miss out on Supercaps.
They've been used to keep SRAM-based non-volatile storage running for decades.
(At least *two* decades anyway)
Almost all Lithium-Ion cell designs regularly 'vent with flame' if significantly overcharged.
- How much is 'significant' depends on the cell design. Liquid Li-Ion is very unstable, Li-Po is pretty stable. "NanoSafe" are said to be even more stable than Li-Po, but they'll still go 'whoosh' if you really try.
The challenge is to make it impossible to overcharge them - every good Li-Ion battery pack has a charge monitor IC that shuts down charging if an overcharge attempt is made.
The dodgy ones skimp on that little detail...
Oh yes. My diesel happily gets over 40MPG on the urban-only commute to work.
On a combined cycle it'll do 47-50 MPG.
Plus I can fit so much more stuff in the boot than you'll ever get in a Prius.
What I don't understand is the complete lack of Diesel-Electric hybrids. If Petrol-Electric is good, surely diesel-electric is better?