I don't think the battery is very heavy...? The cells are maybe 50-60lbs, and the entire module in the back of the car is maybe a bit over 100? So, less than a person in the passenger seat. However, recovering some of the space used by the battery systems could be nice. The battery area really has a LOT of dead space, and if you could pull that out, you'd gain a lot of cargo space.
In terms of fuel economy, I'd say very little - the IMA is more about making the car awesome than more efficient.
The economy argument:
When cruising on the highway, if you need to climb a mild incline or pass, the IMA system allows the engine to stay in a peak-BSFC RPM range, rather than needing to downshift, which DOES save fuel. Same with accelerating - you can keep the revs low and shift early while still accelerating at a reasonable rate, which saves fuel. On the flip side, any energy you use will need to be recharged later, and not all of it will be from regenerative braking; sometimes these cars will slowly background-charge while driving around to make up for an unequal amount of energy spent vs recovered in deceleration, and it's a little lossy converting from mechanical to electrical energy, putting that energy in a battery that has internal resistance and slowly self-discharges, and then converting from electrical, back to mechanical energy. Why have the IMA then? My argument is that you get the same economy of a 3 cylinder, with the acceleration of a 4 cylinder. When the IMA goes, you don't lose the economy, just the extra torque.
If you're frequently sitting at stop lights, auto-stop can potentially save you fuel, but a lot of hyper-milers will shut their engines off coasting up to and while sitting at a stoplight anyway. If you're not the type to shut your engine off frequently, the IMA could save you fuel in city driving.
Awesomeness: It's really cool to be able to kill the engine while coasting down a hill, and then when you drop it back in gear, have the engine spring back to life automatically from the IMA. It's awesome that when your wife/friend/whoever is driving the car and they stall it, the IMA motor brings the engine back to life, or they can even just mash the petal to the floor and accelerate anyway, even after stalling the engine. It's awesome to have all of the torque that the IMA brings, down at 0RPM - I find the Insight quite fun to drive, compared with other economy cars I've driven. It's really great to have a car that has a highly efficient electric motor in place of a lossy alternator - though you'll still have this feature even if you do an IMA delete.
I think you can have your battery refurbished for as little as $500. Sometimes all it needs is one or two cells, and sometimes you can get lucky enough to rejuvenate a weak or "dying" battery with a grid charger you built for $30 from LED power supplies you bought on eBay.
I'd much rather have an Insight with a working IMA than not, but it has little to do with economy.
EDIT: If you get one with a weak or dead battery, I wouldn't get a normal replacement, I'd do what rmay635703 has suggested:
Quote:
Originally Posted by rmay635703
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^ Getting a set of Nissan Leaf lithium cells in this car would allow for HOURS of continuous assist, and the ability to charge it up at home, rather than the ~10 minutes of continuous assist (tops) you would get with a replacement NiMH battery.