Help! Blown 2 CDI’s!

Hi, I picked up a 2007 Kodiak / Grizzly 450 with a bad CDI. Or so I thought it was just a bad CDI at first so I ordered a new one.

I put in the new CDI and it fired up off an old automobile battery I had lying around (ATV Battery was missing). I had planned on loading it into my truck to take to my inlaws acreage to ride it but when I disconnected the battery, the 10a ignition fuse blew and it died.

I reconnected the battery and tried again. Every time I put in a 10a fuse, the fuse blew. After troubleshooting, and 6 fuses later, it mysteriously worked again. So… I disconnected the battery and it happened again. This time the CDI popped and smoked 🙁

Any thoughts? Was it wrong to disconnect the battery? Could I have a bad ground somewhere? I’ve had quads before without batteries and had no problems jumping them like this.

Thanks in advance!