Everything degrades over time, entropy is a rule of the universe. On the other hand, the Prius has a computer whose sole job is maintaining the battery. You will not experience any loss of efficiency as long as you own your Prius.
What my conern is that the battery may not "hold" as much electric after it recharged hundreds of time. Perhaps when the car is in its 5, 6 7 years, FE may drop due to ICE engine has to recharge the battery.
The batteries will slowly degrade over time. The link below is a DOE study on several early hybrids looking at exactly this issue: avt.inl.gov/pdf/hev/end_of_life_test_1.pdf (sorry can't link right now) At 160,000 miles, they found the battery in the '02 Prius' had lost a fair amount of capacity but interestingly they did not find that it had any effect on fuel consumption. Under normal driving conditions the size of the battery is not as important as you might think. I also believe that signifigant improvements were made to both the batteries and the battery controller in the new '04 design so the expectation would be that they would last even longer. Rob
I should also add that the anecdotal evidence is that they will last a very long time. There are a number of first gens up into the 1-200k+ range now and one that even went to 350k miles before it was totaled in an accident. There are some second gens up in the several 100k range now that are being used as taxis and so far they have performed very well. There are a lot of these cars out in the field now, and some are approaching 8 years old (11 in Japan). Stories of battery failure are still pretty rare. The ones I have heard of are mostly related to abuse (driving to very low SOC after running out of gas) or having not received the battery sealing TSB on the early Gen 1s. Rob
When the ability to post a JPG URL returns, I'll post a graph that shows: battery capacity - Ahr decreases charge-discharge efficiency - decreases rapidly and then plateaus for the rest of the Ahr capacity loss Yes, the chart is a little busy but you can see that the round-trip efficiency stays aournd the 70-80% range until the battery capacity started reaching 6 Ahr. Thereafter, it rapidly increased to 90% at the peak. This is consistent with reduced internal resistance as the restored electrolyte had a larger surface area. Bob Wilson
Of all the things to worry about associated with driving an automobile, this one should be near the bottom of the list.
