Dropping hybrid performance

I own a 2006 Prius. For the first year it got city mileabe in the 50’s. Since then mileage has gradually dropped and now gets 45 mpg at best in warm weather and rarely makes it to 40mpg when it’s cold. We posed the question to our Toyota service department at the last checkup. They said the system checked out fine. Any ideas?

Yup, your battery pack is getting weaker… it’s not bad parse, but it’s not holding a charge like it used to. Think about any other type of rechargeable battery, over time it holds less and less energy, on your cell phone this means you have to plug it in more often, on a Hybrid it means the gas motor has to run more often, thus using more fuel. The battery is still “Good”, its just not as good as a new one.

This is the down side to Hybrids, the battery pack does not last the life of the car and is $$$ to replace. They don’t tell you this in the sales brochure.

Change the thermostat and call me in the morning.

How many miles on your Prius? As mentioned, battery pack could be getting weak, engine temperature could be lower than ideal, or the catalytic converter could be degraded, causing the combustion engine to run longer. Also, have you changed tires? Do you spend more time doing freeway driving than city driving?

ASE, good thought on the tires… If you did not put on Hybrid tires it will cost you MPG…

Agree, you need low rolling resistance tires. Make sure the air pressure is adequate. Probably the 6 year old battery though.

How many miles are on the battery??

Contrary to popular belief the batteries can be tested/conditioned or even replaced outright for LESS THAN $600 through salvage yards or but the modules online from $20-$40 each…

If you get a scan tool like the one from http://www.autoenginuity.com/ you can check the voltages and status of each module pair. or you can just pull the battery and get a ballancer like the MRC Super Brain 989 from
for around $89 and then just run each module in the pack through 2-3 discharge/charge cycles and see what the Mah reading is. When new they should be ~7335Mah.

I am upgrading the modules in my 2003 (GEN I) Prius to GEN II (2004-2009 model year) modules and to start with i got a 2004 battery pack from a junked Prius for ~$420 with only ~30K miles on it and I am going through 2 auto cycles (discharge then charge) on all of them now and am getting 7335Mah on all of them. Since my 03 has 38 cells I bought 10 more and am going to swap them out for 10 from the salvage pack and will cycle those as well.

***WARNING: If the batteries are not in a battery pack then you need to lightly compress each battery between 2 boards with C Clamps tays pressure on them as it holds them together.

If you need more information, please reply to this post.