something does not look right to me ...maybe you do have it backwards . I would not drill any holes
Not sure if this may help you are not I put mine in the first Yours looks the it is in the second
From Manual
The spring clip must be engaged in the FIRST stem opening in order to maintain battery compartment access. Hand-tighten the camlock collar. Do not overtighten!
If you have to dislodge to change the batteries, something is definitely not on right. I would gather that you have something "upside down" or backwards.
Disassemble and try again. You will get it right!