After 9.5 years and 135k miles, we recently replaced the original hybrid battery on our 2005 Honda Civic Hybrid. There were immediate substantial benefits.

Symptons of a failing battery had been apparent for the preceeding 6 months. Erratic and poor mid-range engine power, both engine malfunction and IMA warning lights constantly on, erratic fluctuations on the battery assist/charge gauge, poor fuel economy compared with earlier (still better than a non-hybrid!), abnormally quick discharge of the battery on hills, battery charging when it should be assisting.

We got our new battery from Bumblebee Batteries of Portland, Or, who also installed, after doing the usual research. They were pleasant to deal with, price was competitive and battery quality seemed amongst the best. Mileage over the same 600 mile route improved 18% from 40.6 miles/us gallon with the old battery, to 48 mpg with the new battery. Both warning lights have gone out. Mid-range power is back to normal. Battery assist on familiar hills seems to act for noticeably longer than it ever did before, supporting Bumblebee’s claim of more battery capacity than original. Based on my now 800 miles experience with new battery, I also believe that our average mileage will level out at a few percent better than the vehicle achieved when new.

So if you have been postponing fixing your suspect battery, I hope that our favourable experience will help your decision.