Quote:
Originally Posted by Ecky
The 12v runs the normal electronics and the backup starter, which is only used if the IMA battery is dead or otherwise non-functioning. The IMA motor starts the car, both first startup and during auto-start/stop at traffic signals, so that battery isn't actually used to start the car.
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Be aware, though, that ALL the electronics, including the IMA system, work off the 12-volt battery. This means that if it doesn't hold adequate charge, that fully-charged IMA battery won't start the engine. You also can't push-start it if it's that low (or at least I couldn't).
The small OEM 12-volt battery is hard to find (or was some years ago), but the larger battery used in a standard Civic (Group 51, IIRC) will fit the tray just fine.
And FYI, one indication of 12-volt problems that I don't think is documented anywhere is when the brake & battery lights in the instrument panel light up simultaneously. I found this sometimes happens on hard acceleration when RPMs go above 3500 or so. If you have an OBDII reader, normal system voltage with the DC-DC converter charging the battery will be about 14.5V, It should fluctuate between that and about 12.8, but if the DC-DC goes off, it can drop as low as 11.5V before it switches back on.