Why about 30% of 10-15 Prius hybrid batteries may be dirtier than you think.

The 30% is an approximating I have gotten at least 12 10-15 battery packs with Fans from from memory about 4 were very dirty. (Picture at link below.)

The intake grill is just above the rear seat bench. So when the fan is running and anything disturbs the dust on the rear bench it can get sucked into the intake. Also on a 2010 the fan blows straight into the battery so there is no back pressure from a bend and the battery gets as dirty as the fan. This is an issue because the gap between the modules, where the air has to flow is only about .07 of an inch see pictures the dirt and hair at: http://www.elearnaid.com/fiforpr20to2.html

What is the solution. A filter.

Do you need this?
If you never have people or pets in the back seat, vacuum the rear seat regularly, and are never in dusty areas you probably don't need it but even then it is good insurance. For everyone else I would highly recommend this be added to you car. If the cooling air is restricted your hybrid battery can over heat and prematurely fail. Also, there is a filter in the 2016 + Prius.

Frankly at the link above I have provided a filter. It is not just a piece of plastic with restricted holes but a five layer matrix of 1/10 inch holes. It captures most of the dirt and all of the hair and only lets in a little very fine dirt which gets stuck on the fan none observed on the battery. So in the future you only have to clean the filter.

The only downside is the filter does have to be looked at occasionally and cleaned when dirty gray. The filter is right behind the grill so it is easy to see. For more details click on the link above.

 

I have been hand cutting these filter from the 1/10 inch material for at least a 1.5 years and installing them in cars no problems. Because I wanted to use a smaller hole in the filter than the air passages in the battery I tried smaller holes in the filter. I overheated the battery in my car and it degraded significantly when I tried even a 1/4 inch of such material so I know the 1/10 inch hole is safe. That is provided the filter is looked at occasionally and cleaned when not dirty.

 

The amount of air resistance you will get with 1/10 inch holes is far less than the air flow you will loss with a dirty fan not to mention dirt in the battery. If you want to worry about it fine. Or put in a one layer screen which is actually better than Toyota's solution because they used solid plastic and blocked out the opening to a number of small holes.. I have used this material in many cars no problem. When you overheat a battery; the battery degrades in minutes. One hour driving on a hot day and my battery has lost a great deal of capacity. No codes but my battery State of Charge goes up and down much faster than it used to. It is very obvious.

I have driven many hot days with the 1/10 inch holes and noted no degradation then I tried smaller holes - degradation on the first very hot day.

 

One thing I have to repeat. If you do not have a filter on the 2010 thru 2015 Prius and the fan sucks in dirt you not only have to clean the fan repeatedly but also clean the battery. Every time I have taken apart a 2010 to 2015 battery if there is dirt on the fan there is dirt in the battery. The air flows in the bottom so a lot of it sits harmlessly at the bottom of the tray but some of it gets forced up in between the battery modules. Not a good thing! The cooling passages farthest from the fan clog up first and it gets progressively less as you get closer to the fan. The fan sits at the end of the battery tray and the air is blow straight into the bottom of the battery!
Compress air and a long thin brush used to clean out the back coils in a refrigerator will do it but it is a lot of work that can be avoided with a filter. For pictures go to http://www.elearnaid.com/fiforpr20to2.html