The 2004 to 2009 Prius did not come with a filter for the hybrid battery cooling air! Heat will decrease the life of your hybrid battery. Prevent dirt and hair from clogging the fan and prevent dirt and hair from getting in the air passages between the battery modules! There are 168 battery cells in your hybrid battery if one of them overheats and fails you get the red triangle. Unlike other products this filter has seven layers to make it impossible for hair to get into your battery. Also only the finest dirt can get in which causes no problem. All while hardly restricting air flow. This can save you down time and the expense of having to have your large battery cooling system cleaned! Why take a chance on prematurely ageing your battery. Buy and install this filter. Once installed you just have to look at the filter occasionally and vacuum it when dirty. (We provide two stickers to remind you to look at the filter.) Way easier than cleaning the fan and the battery! Installs just inside the grill so it can be vacuumed in place; yet can not be removed by passengers. Made in USA, 50% parts made in USA If you are constantly carrying someone, pets, or cloths etc. in the back seat (Lyft Uber drivers etc.) this is very important The 2004-09 Prius did not come with a filter for the air used to cool the hybrid battery. As a result the fan can log up with hair and dirt and some dirt can get into the crevices between the battery modules. (We also list a filter for a 2010 to 2015 Prius.) The solution is a inexpensive filter! You get a 3/4 inch deep filter with 1/10 inch holes so the air goes through a seven layer matrix. Very little dirt gets through and the holes are big enough (1/10 of an inch) so there is little air resistance. We started selling this product in Jan 2019 and had been hand cutting filters from the same material for 1.5 years for our customers. The filter is held in place with Velcro we include. The Velcro's adhesive is rated to withstand -40 F to 190 F. You also get instructions on the installation and for the 2004-9 the instructions include optionally cleaning the fan and the battery. You also get a sticker to remind you to inspect the filter and see if it has gone dirty gray. In that case can vacuum the inlet. Most of the time that will do it but if it still looks dirty you remove it with one bolt and wash it with water. A garden hose will do. The pictured fan is a fairly dirty fan but we have seen far worse where no air could flow at all. This picture shows the fan with the intake vent removed. You can see that the fan is behind the battery and above it so there are multiple bends. This creates a lot of back pressure so most of the dirt is in the fan. This is bad enough but some gets on the top of the battery where it gets into the small passages between the battery modules where it can restrict cooling air. Our filter captures all the hair and all but the finest dirt so your fan and battery will not clog up. Once the filter is installed you have to look at it on occasion . (The filter can easily be seen as it is just behind the intake between he rear passenger door and the back seat.) When the filter turns to dirty gray vacuum it in place. You can also take it out and wash it. The filter can be washed with plain water (garden hose). It is easy to install. You just lift up one side of the back seat and undo one bolt to get the the plastic grill it fits behind. For the 2004 to 2009 Prius we include instruction on how to install the filter and how to clean out the fan, battery ducts and battery cooling passages. The instructions are set up so you can just install the filter, and also clean the fan and ducts if you choose to. If the fan is very dirty you can also clean the hair and dirt out of the hybrid battery. Why take a chance and have your hybrid battery fail prematurely. Price includes A write up on how to significantly reduce engine oil consumption as well as a write up on how to install the filter and clean the fan and the battery. Comments: Sageman Great idea This is a good and simple way to solve an important problem with gen 2 cars. Very affordable and easy to install. ____________ "I received the package and installed it. Very nice product, I actually like that the filter is inside instead of outside to prevent tampering by people in the back seat." J. R., ELMHURST, IL The installation went fine, thank you. I appreciate your ideas and efforts to help with Prius ownership! ( I bought a battery installation kit from you many years ago too. ) Thanks again and best wishes for a great 2019 and beyond, October 2019: I have vacuumed the filter while in place a few times with a shop vac. We have a German Shepherd (aka a German Shedder) dog that often rides in the back seat and this filter has stopped a lot of his hair from entering the protected area." E. R., Yelm, WA Comments from buyers: The filter fits great! Super excited to find this since I just put in a new hybrid battery to my 08. Plus the paperwork given with some more information about the Prius was very helpful! Thank you so much! Not bad, easy clean Great item, easy to install and gives great peace of mind with a dog in the car Great seller, very helpful. item as described. greater Great item fast service Super Fast Shipping A1 Seller Will Buy Again. Goods as described, well priced, and fast to ship. Thanks Works great! Thank you Smooth transaction and fast shipping. Would recommend. Thanks Buyer: bruwdaddy (179) Great kit and quick shipping! Thanks for the extra reading material too, a nice touch. A+++