Manufacturers suggest that you remove the negative side first, and then disconnect the positive side.
Reason being, if you use a larger / longer wrench in the battery compartment than there is space, while disconnecting the positive side, and you touch the wrench to the body, you’ll short out the battery and possibly have it overheat and ****BAMB**** explode.
By disconnecting the negative side first, if you touch the wrench to the body, nothing will happen!
Reinstall the opposite way, install the positive first then the negative side.
Hope this makes sense to you!