Anything less than a full Tesla-like pack and motor would be a waste.
A 60+ kWh pack could pull a semi over a mountain and regenerate most of it back on the down-slope, saving the brakes at the same time.
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2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
 lifetime FE over 0.2 Gigameter or 0.13 Megamile.

For confirmation go to people just like you.
For education go to people unlike yourself.
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