New or used hybrid battery replacement?

It's hard to answer your question, without knowing whether your priority is to reduce the initial cost of the repair, or to maximize the period of time that the replacement battery will last.

 

Some will and some won't last the life of the car. Obviously some are failing sooner. In my opinion batteries are one of those cases where the old adage of "second hand is second hand" truly does apply.

You always take some chance with a s/h item. You rarely know how it was previously treated or the exact reason why it's currently for sale. How much longer do you realistically plan to keep the car?

 

The other option you may have is Re-Involt.com in North Carolina would give you a rebuilt used batt for about $2100 installed they claim is better than new with 18-month warranty. Also they are working on a Li batt replacement which might be cool, but they have not announced price/availability/advantages yet.

 

Yeah but OP has a "contact" and can get a brand new battery for $2100, which is a very good deal.

Personally I still think it's kind of line-ball on the secondhand battery. Given that the car is 2005 model I do agree with the OP that there is a pretty good chance of even the s/h 75k mile battery going the distance with this Prius.

The new battery is obviously a safer bet, but over twice the price. To be honest, if that new price was $3500 or something that some people have been quoted then I'd definitely be swayed to go with the s/h battery.

 

Well OP said he had a good price on a new battery, but it was unclear if it would have a good warranty. The other idea is give a call to Re-Involt.com to see what they say about the Li battery. If it sounds good, go with the cheaper replacement with the idea to switch out to the Li batt if necessary.

 

To me a second hand battery from a later model 2nd Gen donor for a fraction of the price of a new or refurbished is a good bet. Only a small percentage are failing. I would expand the search area for a used one from a front end collision donor to try to find a less expensive one. I have seen some in $500-700 range. At those prices it would take three failed to get to the stated new/refurb cost.

 

What is your idea regarding what "life of the car" means?

Notice that your original battery failed at 136K miles. The auto industry standard for vehicle "life" is typically 150K miles/10 years.

If you buy a used battery with 75K miles, don't be surprised if it fails after another 75K miles or so. Of course, prior to then you may have gotten rid of the car for other reasons.