My brother and I both bought 2007 HCH's new.
Well, the IMA light has been coming and going for a while now in both our vehicles. Last week, my brothers IMA pack was too low to start the car and his 12 volt battery was drained by his radio. He got a jump and managed to start the car and get home, but the 12 V battery light was on all the time meaning it wasn't being charged.
After much forum scouring, brainstorming etc. we learned that it could be just a bad IMA pack. In that case, the 12 volt battery light should go off at approx >1500 rpm. That wasn't happening however, so suspecting a weak 12 volt battery, we replaced the 5 year old 151R with a new one from the dealer. No luck.
Finally we decided to test the DC-DC converter. It is the one between the Air conditioning compressor control module and the IMA battery pack behind the rear seat.
Testing with a voltmeter with the engine running (and wearing high voltage gloves), we could see an input of >175 volts feeding the converter (upper right thick positive and negative wires). However, testing at output of converter (lower left) positive under the red cover and negative next to it, we were getting only battery voltage which kept dropping. Turned off engine, turned off IMA, disconnected 12 volt battery ground cable at the battery and then removed the negative output from the converter. Reconnected 12 volt battery ground cable, turned IMA back on, started engine and retested output of converter - zero volts.
Figured it was the converter, got a working used one and that fixed the problem.
Somehow the DC-DC converter might have got fried when he got a jump.
Hope this helps someone.

 

While reading up on the forums, I found that there had been a recall on these vehicles for the DC-DC convertor. If it failed, the 12 volt battery could get drained and leave a driver stranded without even hazard lights working. Very unsafe situation. Unfortunately I was told by Honda that neither of our cars fall in the range of eligible VIN's.