If the brake pedal feels spongy or a red light shows
Pull over somewhere safe and switch off. Have the car checked before it goes back on the road. With a hybrid, also stay away from the orange high-voltage cables: they're not for anyone but a trained mechanic.
Which Prius is it?
Limited sales began here in 2000, with the official launch at the Sydney Motor Show in October 2001. The first and second generations used nickel-metal hydride (NiMH) batteries. The fifth generation wasn't sold in Australia, so every Prius bought new here is an earlier design, and most have some age on them.
Tell the mechanic the year and whether it's a standard Prius or another model in the family. It makes a difference to the pack, the parts and the schedule.
Toyota Prius hybrid battery replacement
What a good mechanic does first: scan the hybrid system, look at how evenly the pack's sections hold charge, and check its cooling. A blocked cooling fan or duct can make a healthy pack run hot, so ask whether that's been looked at.
If the pack does need replacing, the estimate should say whether it's new or reconditioned, what warranty comes with it, and what checks follow. On a car this age, compare that with the car's overall condition. A mechanic should be willing to tell you if the rest of the car is worth the money.
Your 12-volt battery is separate. The low voltage battery powers the computer and accessories, and if it fails, the car won't go, however healthy the hybrid pack is. Test it first, since it's the simple fix.
Engine light on a Prius
A steady orange engine light means a fault's been stored. It isn't automatically the battery. On a Prius the computer watches the petrol engine, the hybrid system and the brakes together, so one light can have many causes. What an engine light means covers the first steps.
Older cars have recalls worth checking. CarsGuide reported about 1,652 third-generation cars from 2008-09 recalled in June 2013 for a brake booster pump that could leave a spongy or longer pedal. In February 2014 it reported 5,500 Australian cars built 2009-2014 recalled for power converter software that could bring on warning lights and limp home mode. CarsGuide's Prius page doesn't list a hybrid battery fault. Run your VIN through vehiclerecalls.gov.au.
Servicing a Prius
Toyota's petrol hybrids sit on 12-month or 15,000 km intervals, per CarExpert, though an older Prius may differ, so check its book. A hybrid still needs oil, filters, tyres and brake checks. The brakes rarely work hard, thanks to the electric motor, so ask for a look at how they're moving, not just how much pad is left. A local mechanic who specialises in your car.
If it were our Prius
We'd pay for a proper hybrid health check before agreeing to a new pack, and ask for the results in writing. Then we'd weigh it against the car's age, its rust and its service history. If you're buying one used, do that check before you hand over any money. A good mechanic will tell you honestly whether it's worth doing.