I bought my DJI Phantom 4 Pro drone and love it! I even bought 2 extra batteries and the 3 port DJI charging station so I'd always have a charged battery and others charging. Well the one thing with it is that with any LiPo battery that during high discharge the pack gets hot (No not like exploding hot) and when you're ready to throw it on the charger you have to wait for it to cool off before it will charge (the battery is so smart it won't even accept a charge until it cools down enough to charge it safely). A major improvement on the Phantom 4 batteries compared to the Phantom 3 batteries is that there are air cooling channels between the LiPo cells allowing faster cooling and also to reduce heat transferred between cells. Well I saw this and thought "Now if I could blow cool air thru these it would cool off faster!" And POOF the idea and final design of the Bat Cooler came to be!
I used a small computer CPU cooling fan I had laying around and cut the JST power plug off it and soldered on a female barrel power connector so I could use a standard 12 VDC wall power supply to power it. I haven't installed a safety screen on it because it is so small I really don't think it needs it. The internal fan diameter is 67.85mm so I'm not sure what that makes the total "Fan Size", the side to side measurement of the fan is 72mm square. The fan is set to blow inwards, in other words the airflow is thru the fan, thru the battery, and out the oval exhaust ports.
One side of the end of the battery has more of a hangover then the other side does, this goes down into the fan enclosure and the shorter side goes into the side with the notch. You can see this in the pictures.
Side Note: If you make a 12 VDC power cord with either a cig lighter plug end or alligator clips on it you could use it with power from your car or truck.
UPDATE: As per a request I modified the original design to now accommodate 2 batteries to be cooled at once. Now that's it's longer in length some printers may not have a large enough bed if laid as shown, like wise standing it up some printers might not have the Z height (vertical) to print this. Your print software if set will tell you if it is too big one way or another.
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I stood it up in orientation so it would be easier to print but you can change that if you like. I used a raft because of the oval cooling ports that I wanted to come out nice. I used supports for obvious reasons. Printed it in ABS for strength beings this would be taken everywhere my P4P Drone was taken.
Remove the inside supporting material, clean the exhaust ports (if your printer has an issue with stringing). I left a little "Wiggle Room" in the opening where you insert the battery so it fits nicely but won't bind when pulling the battery out, you many have to trim the opening depending on the final print on your printer.
I designed this with AutoDesk 123D Design and printed it on my FlashForge Creator Pro using Simplify3D (S3D).