Things to remember:
The 2004-2009 Prius battery has 28 separate cells. Consider it a multipack of batteries wrapped into one Hybrid battery.
Trying to repair a Prius battery without the proper knowledge and safety equipment could be fatal. ( 200+ volts is dangerous)
Costs associated with a 10+ year old hybrid battery will increase with age.
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ALL BATTERIES EVENTUALLY FAIL !
What you have to consider is each of the 28 cells in your Prius battery is a wear item and will fail over time. Imagine you have a large flashlight with 10 batteries in the handle. Over time the cells will fail, and they will fail at different rates. When one falls below a certain level of strength, the flashlight will no longer turn on. With the proper equipment you could test all of the cells and replace just the bad cells – let’s say you replace 2 of the cells. Now your flashlight works again, but you have 8 other cells that are also worn and they will fail over time. Even the 2 you replaced will eventually fail. The only question is when each of your 28 individual cells will finally fail to meet minimum performance levels and it has to be replaced.
The practice of reconditioning a hybrid battery is perhaps a reasonable solution. We test each of the 28 cells by charging, putting a load on, and charging again. Cells that fail to meet a minimum standard are replaced with other used cells that still meet minimum standards. When all cells meet our minimum standard we call it a reconditioned battery. Over some period of time all cells will fail and must be replaced.
Deciding between the price of a new Prius battery
vs. and a reconditioned battery is mostly economic. If you need a less expensive solution until you can afford the cost of a new battery, then a reconditioned battery may be your best option. If you have the ability to invest in a new battery, that is a long term solution. However, those new battery prices are beginning to diminish so a new battery might be the right long term choice.