Since we bought the Insight, I have wondered about replacing the battery pack. It has happened.
At 112 k miles the IMA light appeared on the dash. The service rep said the battery pack was deteriorating.
Months ago I had read online chat, to the effect that Honda was extending the warranty on the battery pack in six states, from 80 k miles to 150 k miles.
Fortunately for me, Honda now has extended the warranty in all fifty states. Otherwise the bill would have been around $5 k.
Honda was nice to me. ..The service department had its own complaint about Honda: Honda only allowed them one hour for the labor....
As a side note, the struts had given out on the rear hatch. Replacement struts had been on order for weeks. I had to prop the hatch with my shoulder or my head when loading bags of litter into the hidden compartment. But when the technician needed to access the rear deck and the battery pack, the struts arrived quickly.