Thermal paste to help cool aging traction battery.

Well I finally made an account, strap in it's going to be a long one.. I got my Prius a little over a month ago and I love it to death, however at 142k miles the battery has seen better days.

While it's balanced well (all within 0.42v) , the Internal resistance is between 26-32 which is fine for short trips but I drive for Uber eats and grub hub in California and if I don't have the battery's blower fan and a/c at full blast it will easily get into the 120s practically disabling Regen and ruining my mpg.

I've even gone as far as hooking up the passenger a/c duct directly to the battery fan intake which helps alot but isn't exactly an elegant solution...

I've also looked at teardown videos and even partially disassembled mine (blower fan and exhaust port only) to get a better understanding of why the center of the battery can at times be 30° higher than the outer parts.. a bad cell it ruled out because of the aforementioned 0.42v voltage difference between cells

My theory is that the center gets so hot because the fan only blows air on the top and bottom of the cells and not the sides or in-between. It's also insulated by all the other cells.


My question is,
Could non conductive thermal compound be dangerous in any way to the future of the hv battery?

I'm thinking about putting a thin layer in-between each cell to help spread the heat evenly.

Ps. I know I can just get a whole new pack but I'm looking for a temporary solution while I save up for the Dr. Prius lithium pack

 

I guess I didn't look hard enough lol. those diagrams are exactly the things I was looking for. Had I seen them I wouldn't have made this post...

Looking at that gen 2 diagram makes me think though, why does the gen 2 battery vent outside directly but the gen 3 just dumps it into the spare tire cavity? Is there some exhaust port I'm not seeing?

 

Wow that's incredible for 200k. I've done the drprius battery health check and the highest result I got was 60% I guess the previous owner really ripped into the charge cycles.

Which makes sense if he did Uber eats or something similar because there's a lot of down time and in California summers you need AC which means lots of charging and discharging if you are parked waiting for an order.

 

It only gets to 32 when the battery gets really hot like 115+ which no longer happens because of my a/c mod. I'm going to be going on a trip today so I'll record my findings without it and get back to you. I was not expecting this level of hospitality!

I think my first step will be checking for bad blades. I don't have a thermal camera but I do have a laser thermometer. If I need a t camera I would rather rent one.

Second will be full disassembly checking busbars blowing dust out (the fan filter had ½ of an inch of fibers and crap on it when I bought it)

I have been shocked enough times throughout my various hobbies to know not to mess with 100amps continuous output at 200V without proper gloves.

I'll also look into reconditioning and how that works.


This is my first car and I got it for 11k I may be able to contact the dealer and ask why I was told "it has a brand new battery" when clearly it's not anywhere close. Maybe they meant the 12v?

 

Just got back from my short trip and the numbers are a little different. I guess I just remembered wrong, [ Trigger warning for advanced google sheets users, I know its bad ]


Note; I had the battery fan on full blast without the A/C pipe connected to the intake. However, the A/C was set to low.

The chart on the left clearly shows my temperature problem, 124 degrees at its highest. granted I was regening down a hill at 70mph.
Yes I know it's not exactly the same as driving all day doing what I usually do on my job but, drive long enough without the battery fan on full blast with ac and it will hit 120+

The bottom chart shows that there is way less voltage difference than I stated in my original post. The highest I saw while not accelerating or decelerating was 0.10V maybe cell 1 a little bit but that wouldn't be

The chart on the right shows that no one blade is particularly terrible in the internal resistance variance department. they are always within 1 of each other. weird that The IR flatlines as temperature spikes. I was not expecting that.

I looked into battery reconditioning and wow that is way too much time (without buying an expensive balance charger) and just barely in my range of electrical understanding. will definitely be a last resort if I can't find any bad cells.


I won't be home until next Monday so that will have to be when I do the battery disassembly.

 

@ChapmanF

Good to know!

@Grit

cant edit it after posting. unsure what you meant by the emoji.. is that in response to the ac mod or me not knowing internal resistance is not directly correlated to temperature.

By ac mod, I meant a literal air duct from home depot connected to the passenger side airport all the way to the intake of the battery. Yes, I know....but it works. up to 30 degrees of improvement

Of course, I would rather not have it but, it's required at this point which is why I made this thread.

 

Pictures of the results or how it's hooked up?

Don't really need pictures I used a 3inch in diameter 25ft long air duct from home Depot (17$) and duct tape. luckily the duct tape I have matches the interior.

It routes down to the passenger foot well Left along the floor then it just barely fits under the passenger seat and connects directly to the battery intake.

This setup is best for if you regularly have a passenger up front. It is still easy to get in and out and you still have some leg room.

Lastly you can take some towels/old shirts that match the interior color and wrap the tube in it where it's visible. This insulates and slightly masks it. You will need to do this especially where it connects to the ac vent because the shiny tube makes it difficult to see out of the passenger side mirror in the day time because of the glare on the window.

If you want raw cooling performance and love all the extra attention this gives you, then lay the passenger seat all the way back and hook up the duct in a straight line to the intake then wrap some foam around it to insulate. Don't expect to be able to use either seat or your passenger side mirror though

 

I didn't modify the A/C unit itself at all.