I just bought this 08 Prius (66,000 miles) two weeks ago. In the last week I've noticed that the battery goes from 2 bars from full to 1-2 bars in the purple typically within the first mile of driving. Afterwards it tends to recharge back up to green and stay one bar from full for the rest of the drive. Last night, I tested the 12V battery at Autozone and they said it needed to be replaced. Fixed it last night thinking it would solve my issue with the battery declaring rapidly when I first start the car up. I'm still having the same issue today. I'm not sure if I need to get the hybrid battery tested. I checked the battery level using the car's diagnostic and while in park and driving it was hovering at 13.9 V. While it was in standby it was at 12.8V. Images attached!
welcome! the battery icon is not for the 12 volt, it is for the hybrid drive battery. it sounds pretty typical for a 14 year old battery. (they deteriorate from age, not from use) if it starts rapidly fluctuating from high to low to high, etc., you'll know it is on its last legs.
The 13.9 volts in READY just means that the 12V charging system is working. It has nothing to do with the health of your hybrid battery but the quick and extreme fluctuations of the hybrid battery state of charge indicator does tell you that your hybrid battery is just about done for. Perhaps @PriusCamper has some advice. He's more or less in your neck of the woods.
What you're describing is a loss of charge capacity in your hybrid battery. This is a normal occurrence in nickel-metal hydride battery packs and with reconditioning you can restore the pack from what currently sounds like 60% capacity, back up to 96% capacity with three deep discharges and three re-charges. You can keep your battery pack going for many years longer than most packs if you do this maintenance every 18 months. Here's the science of it: BU-807: How to Restore Nickel-based Batteries - Battery University There's a shop or two in your area that do it but they charge unreasonable prices because they'd rather sell you a new battery pack for $2K instead. Alternatively, it's very much a DIY project if you or a friend are up for it? It really comes down to how much money you want to spend. This spending spectrum at one extreme is a state of the art full Lithium upgrade that will improve the hybrid system's performance in every way and give you peace of mind for the rest of the car's lifespan. At the other end of the spectrum is spending a $100 and DIYing a high voltage trickle charger and light bulb discharger so you can do the reconditioning work the pack needs to restore it's capacity. Anyways, I'm an hour or so North of you and might be able to help...
I have the same thing here on my 08 As I’d like to keep this car going for ALAP I’m leaning towards a NPB and just selling my old battery. Let me know how YOU decide to solve your problem. Thanks.
