The Honda Insight’s battery pack is made up of 120 Panasonic 1.2-volt nickel metal hydride D cells. it is capable of 100A discharge, and 50A charge rates. The system limits the usable capacity to 4ah to extend battery life. Total battery pack output is 144 volts.
Honda Insight - Wikipedia, the free encyclopedia is another page to check out.
the pack you have has the batteries welded together, so they are not just normal "D" size flashlight batteries.
for about $1,600 or less you could replace the whole battery with litium, half that if you kept the 4amp hour restriction, or reprogram it and get twice the range out of the battery.