Skip to main content

Spot A Failing Hybrid Battery For Toyota Prius In 3 Ways

If you are suspecting a failing hybrid battery on your car, here are 3 ways you can know for sure if your battery is failing.


No hybrid owner wants to go through the hassle of replacing the hybrid battery. The cost to replace (depending on what you replace it with) can be staggering.

I preach battery maintenance, but not everyone listens to me because they think the cost is too expensive. Then those same people end up putting a battery in their car for two or three times what the equipment costs.

We are not here to talk about what people are not doing but rather how you can tell if your hybrid is about to lose the battery. Here are three telltale signs your hybrid battery is failing (and what to do about it)

Sign One: Suffering MPG
Hybrid owners are very in tune with how their car functions and what fuel economy it gets. While environmental factors play a big part in how much fuel your hybrid is sipping, owners know abnormal mpg drops.

2005 Toyota Prius Fuel Economy Consumption

Fuel econ becomes a factor due to the reduced capacity of the battery as it ages. If the battery cannot store the same amount of energy it did when new, how do you expect it to get the same fuel economy?

Suffering MPG can be caused by many factors, though, so before you go ruling out the hybrid battery, check the other two options I will list in a moment.

Other essential information to keep in mind is what routine maintenance has been done and what the tire pressure registers.

Sometimes the small things make the most significant differences, so check the car over, get a fuel additive, and do all the other items you have put off. Your vehicle will thank you.

Sign Two: Battery Level Fluctuation
A strong battery in your hybrid will be able to maintain an aggressive load. When going up a long hill or passing another vehicle, watch the battery monitor see how rapidly it falls.

A poor functioning battery will fall rapidly under load and consequently also refill quickly during regen braking. Your Toyota Prius or other hybrids have a battery monitor you can watch under these conditions.

2005 Toyota Prius Battery Monitor Depleted

The rapid rise and fall are a sure sign of failure even if the car has not yet posted the trouble code in the comments. Rapid battery fluctuation is a resolvable issue with reconditioning the battery, but you need to address it soon enough to reap the benefits.

Sign 3: Use Dr. Prius App Tests Or Free Version
Dr. Prius App has quickly become my favorite tool to use on a hybrid. It gives you real-time data and has built-in testing features. Recently, I bought a Toyota Camry Hybrid and was under suspicion that the battery was failing.

After using my handy Carista OBD tool and connecting it to the app, I could easily see where the battery was weak. Can you spot the trouble area from the picture?

Dr Prius app for your Toyota prius

Dr. Prius also has battery life expectancy tests you can run to determine how well your Toyota hybrid is performing.

Hybrids are all relatively similar when it comes to how a battery is failing. New hybrids and those with Lithium-Ion batteries are slightly different, but they will show you similar signs.

Also, and this is very important, a "full green battery" on the monitor in your Prius does not mean the battery is healthy. If it goes into the green often, you can be looking at a failing battery.

A failing battery can be remedied before it craps out completely by reconditioning. If your battery is too far gone, there are other, better options like lithium conversion that will make your Prius feel better than new. Or, of course, you can do an excellent remanufactured battery from a reputable place like Bumble Bee Batteries (more to come on this remarkable place).

Any way you look at it, your battery is destined to fail one day, so be prepared to swap it out.

Thank you all for reading I look forward to seeing you in the next article. If you need a hybrid battery for your Camry you are not alone.

Check out this wild new battery tech that Tesla has and why it will forever change the auto industry.

Peter Neilson is an automotive consultant specializing in electric cars and hybrid battery technologies. He holds a Bachelor of Science in Automotive Service Technology from Weber State University. Peter can be reached on Linkedin and you can tweet him at The_hybrid_guy on Twitter. Find his page on Facebook at Certified Auto Consulting. Read more of Peter's stories at Toyota news coverage on Torque News. Search Toyota Prius Torque News for more in depth Prius coverage from our reporters.