Just bought a 2010 Hertz GenIII w/44,000mi. Wife had trouble starting it twice with weird messages like place car on flat surface to orange triangle. I hear it may be a weak battery???
There are several batteries in a Prius The HV Battery is the big expensive one and is not your problem today. It has a 8 year/100,000 mile warranty, if it was. The 12 volt battery is sized small in a Prius as it does not start the engine. Sadly, it does not recover very well from leaving the lights on, door ajar, dome light, radio on, etc. Once it is dead, it never seems to recover. For about $130 you should be able to buy another one at a Toyota Dealer's parts department, it will be even more if you have them install it. For about $170 you can buy a elearnaid installation kit and a 'normal' Optima YellowTop battery, which will recover from being fully discharged better than the stock battery. For about $200 you can buy a YellowTop that is customized for the Prius. When the doors or ignition quit working that is the Fob battery, a 'watch' battery under $5. Toyota Prius 12 Volt Auxiliary Battery with install kit for 2004 - 11 Optima BatteriesOptima Batteries DS46B24R YellowTop Prius Auxiliary Battery
I've had similar issues with my car (although I haven't had the start on a flat surface message in a very long time). When I started monitoring my battery voltage, I've noted it was low. It has steadily gotten lower over the last 12 - 18 months and on advice from folks here, I've purchased a new Optima battery. There was speculation that Toyota got a bad batch of OEM batteries and yours might be one of them. It could also be due to prior abuse (as Jimbo has pointed out). Good luck, while not a cheap replacement, it will give you peace of mind and you may even see some MPG improvement. But the former outweighs the latter.
My (company) G3 is on its second 12-v "start" battery. The first died after six months (IIRC) with zero battery depletions, and it was a new car with me as the only driver. If you're worried about it enough to post the question, I'd replace it, especially since your G3 was "gently used" before you bought it. It's not cheap, but since you're not the only driver, it might save you in the long run if you know what I mean. Good Luck!
