So, for lack of other more interesting things to do, I researched further and found that the Civic Hybrid IMA (Integrated Motor Assist) battery is indeed made of D-size batteries, and not C-size as I surmised. However, as the price of even rebuilt battery packs is so pricey, I wonder if these are better built than consumer-grade batteries in order to handle higher currents, hence more expensive.
Something more to look into...
PS. OK, here's the difference. Regular D cells can handle 10A current continuously, and 50A intermittently. The IMA battery cells can handle higher currents up to 100A, though I am not sure for how long. It still shows that these are specially built, hence more expensive.
What I find curious is that even at 100A peak current, the power put out by the electric motor is just 15HP. And then, at that max current the battery would be depleted in a few minutes. So, it is mainly used to allow a smaller gas engine to be used for better gas mileage. Or the electric motor provides a lot more torque early at low RPMs to allow better acceleration from a smaller gas engine.
Anyway, as the battery is made of 120 batteries in configuration of 20 sticks of 6 batteries each and perhaps only one stick fails, some guys show how it can be disassembled, the bad stick identified and replaced. All can be done in one's garage if he has the time. It is not feasible to replace a single cell as cells in a stick are welded together for the 100A current rating, but pulling out a stick involves just unbolting its terminals. Something an ER/tinkerer might want to do...