Though having the greatest power and energy density (very desireable in an electric vehicle) and excellent throughput efficiency (all-round desireable), Li-xxx batteries are rather expensive in terms of cost/energy(over the lifetime).
Posited is that some common driving patterns lend themselves quite well towards using more than one chemistry - in terms of cost-efficiency over the lifetime of the vehicle - even considering the extra energy expended because of in/out inefficiency and added weight.
If the first few kWh a (sub)urban vehicle which spends most of its time running to the store, or kids' hockey practice, or on the work commute, were from a cheaper (in terms of lifecycle) battery, then the Li-xxx packs could be smaller, and would last much longer.
The two chemistries which immediately pop into mind are nickel-iron (expensive but lasts forever) and lead-acid (very cheap to replace). Use a battery pack of either for short runs, saving the expensive pack for longer sojourns.-- FlyingToaster, Dec 21 2015 Mr. Fusion http://backtothefut...com/wiki/Mr._FusionBetter. [8th of 7, Dec 21 2015] <link>-- 8th of 7, Dec 21 2015 [8th], I don't see how either of your links relates to this idea.-- MaxwellBuchanan, Dec 21 2015 I guess one type could run ancillaries such as air conditioning. Some types are better at fast charge rates (regen braking). Good idea.-- Ling, Dec 21 2015 [Ling] Good idea yourself, but I was thinking more along the lines of powering the motor. Roughly (,subject to algorithm andor operator control) ...
The lo-power pack is always on; charging the oversized regen-supercap when it's not being used by the motor.
The motor runs on the lo-power pack, supplemented by the supercap, which has stored energy from braking regeneration, as well as being "trickle charged" from the lo-power pack when the motor's need is low.
If the cap temporarily runs dry and more power is needed than the lo-power pack can provide, then it starts using the hi-power pack as well.-- FlyingToaster, Dec 21 2015 random, halfbakery