I had the IMA battery replaced in my 2006 HCHII under warrenty. It seems as though it was defective from the factory as the car only had 1,880 miles when my IMA light came on. Battery was replaced with an instock HCHII and has been running perfect since.
Lute Riley Honda in Richardson Texas quote $6,400 parts and labor to replace the battery pack, BCM unit, MCM unit. My warranty was good to 80,000miles/8 years. I was just shy of 94,000 miles after 5.5 years. I heard that Honda has been pretty good about practacticing good will in these circumstances.
Re: Battery Replacement
