If you are considering buying a used hybrid vehicle, you'll want to read this post and do the research on battery life before making a purchase. I thought I would share my experience below.
I was in the market for a used Toyota Prius a little over a year ago. The Gen II Prius built from 2004-2009 was within my budget so I began research on what to look for in a used hybrid. My biggest concern was the hybrid drivetrain and battery.
It is important to note that any battery, no matter what chemistry or size, is a consumable. It will eventually wear out. I just finished replacing the 9 volt batteries in three smoke detectors in my house. This is an annual routine for us and doesn't break the bank at a whopping $10 per year. However, replacing the high voltage battery pack in a hybrid vehicle is a completely different proposition. They don't have a trap door for replacement and the batteries are thousands of dollars for a new replacement.
After much research, I found some reports of cab companies getting over 500,000 miles on a HV Prius battery pack. I also searched forums and automotive sites and couldn't find any complaints of battery failure on the Gen II Prius. (there were a few complaints for the Gen I Prius but they improved the battery pack in the new generation vehicle) I found a 2004 Toyota Prius that was owned by a Toyota mechanic and had 130,000 miles on it. I had it checked by a Toyota dealership and made the purchase.
After performing a bunch of maintenance on the car to recondition it, my wife enjoyed driving it trouble free for 6 months.
And then the unthinkable happened.
I noticed the fuel mileage dropping into the thirties for about a week and then my wife called me from the school parking lot saying that the dash was "lit like a Christmas Tree." She limped it home and I checked it out. After a little research, all indicators pointed to a failed HV battery pack. One trip to the Toyota dealership confirmed my worst fears. The battery pack was dead.
I was quoted around $3200 to replace the pack at the dealer but decided to drive it home. After some searching 6 months later, I started finding new posts of Gen II battery failures from a lot of sources. I did some calculations and realized I was about 6 months out from having the first Gen II Prius hit the 8 year mark when I purchased my used Prius.
To make a long story short, it looks like mileage isn't the primary factor in hybrid battery wear. It appears to be age and environment. From personal experience and from research, if you live in a warm, humid climate (I live in the Southeastern United States) and park your Prius outside of the garage, you can expect to have the HV battery fail after about 8 years regardless of mileage.
After reviewing some of the posts from cab companies that were getting 500,000 miles out of an HV battery, I realized the cab companies were in Canada and they were putting over a hundred thousand miles on the cabs in a year!
If you are in the market for a used Prius, make sure you find out if the HV battery has been replaced with a new battery before you purchase. If not, make sure you factor this into the price you pay for the car. However, if you already have a Prius approaching 8 years old, you may want to consider buying a remanufactured battery and installing it yourself. This is the route I chose for my Prius and below is a video of my installation. This ended up costing around $1800 and the equivalent of a half day of labor.
NOTE: If you are going to replace the HV battery yourself, you must be experienced at working with high voltage electronics or wiring. Improper handling of the HV system in the Prius WILL KILL YOU if you don't know what you are doing. Make sure to watch all three parts of the video before deciding if you have the experience to do this yourself. If not, you can still purchase a remanufactured battery and have a local hybrid repair shop perform the service.