Knowing when the Prius is not getting good battery/Gas mileage

We have bought a used 2005 Toyota Prius. As usual when you buy a used Hybrid, you worry about the battery and its system. How can you tell when the battery system is not running efficiently? We watch the energy screen and are curious when the battery should do most of the power to move. It is not often when we see the battery show Green. It is mostly under half. We do not think the battery is dead, just not up to good expectations.

Did the previous owner leave the Owner’s Manual in the glove compartment?
If he/she did, I can assure you that this topic would be covered in the manual.
If you are not in possession of the Owner’s Manual, you should be able to download it from Toyota’s website.

All car owners need an Owner’s Manual to at least some extent, but owners of hybrids absolutely need to have–and read–the manual.

Anyone buying a 10 year old hybrid should plan on putting in a new or rebuilt hybrid battery and factor that into the price paid.

I would check out the charging system for the hybrid battery. It may be the faulty component here.

You might post this question over on the priuschat forum, I imagine a lot of folks there know how to check the condition of the battery.

What mpgs are you getting?

@texases asks the right question. Check you mpgs with every tank of gas. Use the trip odometer set to zero at every fill-up and write the miles down and how much gas it took to fill the car. If the trip odometer doesn’t work, use the regular odometer and subtract the miles driven between fill-ups. Divide the miles by the # of gallons, that is your miles per gallons or mpg. Do this for about 3-4 tankfulls. Look up on or edmunds,com the mileage that the EPA figured this car should be getting. That will tell you the condition of the overall car.

If you do mostly city driving and the mpg’s are way down from what the car should be getting it is very likely the batteries are getting used up. Stop-start city driving is where the batteries are used the most. Highway driving doesn’t use the batteries much so it shows the condition of the engine more than the batteries.

I would absolutely recommend visiting for more information and insight. The community is very scientific and technical (lots of engineers) who can and will help you with your questions. They will be technical, so try the best you can to get them actionable data (having a battery meter would be a start, knowing your MPG’s and such is helpful, knowing how old the small, 12 volt battery would also be good knowledge too).

If a main battery problem were detected, the main battery warning light will come on. Until then, start saving for a replacement main battery ($thousands$)

Our 2009 Prius also rarely shows green. Situation normal. It almost always shows blue. But almost always over half. I think it only shows green after a long highway drive. Anyway, the computer controls the degree of charge and it knows better than I do what to do.

FWIW our dashboard display always shows gasoline MPG. I notice it gets better now as the weather is getting warmer.

Weather certainly has a factor in mileage. Another thing to consider is that the catalytic converter may be getting weak. Not degraded enough to set a fault code, but a weak catalyst will cause the engine to run more/longer and that will certainly affect fuel economy.