Q: What do hybrid batteries look like, and how do they work?

Gary Smith: Toyota’s high-voltage hybrid batteries are collections of prismatic modules in strong protective cases bolted under or behind the rear seats. In a current-generation Prius, the battery case contains 168 1.2V batteries in groups or modules of six that are slightly different in shape but not much larger than the batteries in an 18-volt cordless electric drill. The entire pack, which includes some relays, solenoids and the metal case, measures about 14 by 36 inches, and is eight inches high. You might picture a suitcase weighing 110 pounds. Because the storage space is different in a Highlander hybrid, its batteries are in three smaller cases. So, picture three attach? cases with a total weight about the same as the case in the Prius.

These nickel-metal hydride batteries are charged by an internal combustion engine (ICE) driven generator and/or by regenerative braking that captures power from deceleration and braking.

Q: Do they ever run out of power?

GS: No. A computer makes sure the batteries never discharge completely. They never fill completely, either.

Q: Are they charged at the factory?

GS: Yes, they need to have enough of a charge to start the engine the first time. After that, the batteries are charged by the vehicle’s systems. Every Toyota hybrid also has a battery similar to the one in a conventionally powered car, but it’s used only for 12-volt accessories and to power the vehicle’s computers.

Q: Do the high-voltage batteries ever need to be checked or serviced by the owner or by a dealer?

GS: No, there is no scheduled maintenance for the batteries.

Q: How long do the high-voltage batteries last?

GS: We designed them to last for the life of the vehicle. We’re aware of owners who have racked up a quarter-million miles without replacing the batteries.

Q: What would it cost to replace a complete battery pack?

GS: Less than $3000, plus labor.