Prius 12V Battery is a Wimp

While the Toyota Prius may be a beautifully designed and engineered automobile, monkeys could have done a better job thinking through the design of the 12V accessory battery (which powers doors, lights, fans, radio, alarm, etc.) So writes Bruce Stenman, who has gripes about his 2007 Prius:

“Located in the rear of the car, this puny battery is about half the size of a comparable sized car battery. To replace it, the rear hatch has to be opened, a cover for the compartment that houses the spare tire removed, and the usual battery cable connectors along with a few screws and subassembly loosened. So arduous is this process that when we brought my battery into the dealership, the service person told us that we were the first Prius owners to succeed in removing it from the car ourselves.

Replacing the battery may not be such a big deal if the battery actually were designed to last a reasonable time period [Toyota’s website quotes 5 years], but the battery failed in my Prius in Monterey, California (hardly a hostile climate) after 30 months. So catastraphic was the failure that even with a charger attached I could not get more than 2.5V from it.

This in itself is bad enough, but wait! There is more.

When the car is at a stop, the engine shuts off. At this point it is necessary to also kill the power, as given the remote control entry system there is no ignition key to remove. If the power is not turned off, the battery is drained completely. There is no circuitry to detect that voltage has dropped or that the car is not in motion for hours at a time.

Once the battery is drained, you can of course no longer open the rear hatch to get at the battery to charge it. You have to crawl to the back of the car to access the latch handle located inside the hatch door. Did no one think about locating a hatch release near the driver’s seat, a common feature in many cars?

For such a critical item, it seems that more care could have gone into the design of the battery. For starters, easier access to it. And a battery with a longer useful life or one that does not fail completely would be ideal.”

There is a kind of irony in the fact that a car featuring 1310W of total energy in its main battery system, can be shut stopped short by a wimpy little 12V battery!