[mpg_numbers_guy]

I've strongly considered doing something like this on my Insight, as I've seen about a 10%/10mpg improvement with my Meanwell pseudo-alternator turned off. Problem seems to be that the 12V battery can't hold any significant amount of regen, so one would need to drag the brakes for a long time to get ant usable regen - one couldn't just tap the brake once and throw in as many amps as would be necessary to charge the battery. I also rarely brake, so my braking isn't more than a quick tap every now and then anyway.

Supercapacitors sound like a possible solution, but I am not knowledgeable enough on them to know how they would work in a situation like this. If supercapacitors would work, and actual regen could be used to the 12V battery, that in combination with a small solar charging setup might be able to eliminate alternator need except on highway trips. The real goal would be to eliminate having to plug in the 12V battery at night, since saving fuel cost at the expense of additional electrical cost isn't a money savings.

What deep cycle battery did you go with?