I custom built a battery lock case by buying one of those cam lock, and putting a metal hinge on the top https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=cam+lock&rh=i%3Aaps%2Ck%3Acam+lock
You want to be sure to get the correct measurements <----- in this or potentially ruining your bike
You also want it to be a tight fit....
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Also I recommend having 2 locks for the front and back wheels
The first being Alarm lock that will scared off thieves https://www.amazon.com/s/ref=nb_sb_noss_2/135-5617140-5383263?url=search-alias%3Daps&field-keywords=alarm+locks
Second being a standard lock https://www.amazon.com/s/ref=nb_sb_ss_c_1_4?url=search-alias%3Daps&field-keywords=kryptonite+bike+lock&sprefix=kryp%2Caps%2C186&crid=25Y51EH0EGK47&rh=i%3Aaps%2Ck%3Akryptonite+bike+lock
More locks here