You might want to just ask this in a general forum as it applies equally to all hybrid cars, not just the HAH. My opinion is that economies of scale, and also further research, will cause battery costs to drop drastically over the next 5 years or so. If that is true, by the time you need a replacement pack it won't cost that much. Maybe we can hope for $500 or $1000.

All cars if you keep them a long time can end up needing expensive repairs. Yes, the battery is just one more thing that can wear out, so it is sort of a minus, but maybe the hybrid assist will mean the engine gets stressed less (for example when speeding up), so maybe it needs less repairs? I don't know, I guess we will see.