How do you replace the battery in the bsa hmrgbd30

The large knob on top holds the battery. Should be a slot that a coin will fit in to remove the cover.

I've never had that problem with my scopes, but BSA's customer service department welcomes questions and comments. I bet they'll have some good advice. Here's their contact information:

954-581-2144 (Monday - Friday 8.30am - 5.30pm EST)

BSA Optics, Inc.
3911 SW 47th Ave. Suite 914
Ft. Lauderdale, FL 3331

no it dont need a battery to get the spark this engine has a magneto under the flywheel check out the coils in the magneto first also check that the flywheel magnets are good and strong this all ways was a week point in this engine

remove the screw on battery cover counter clockwise.  Replace the small button battery and carefully replace the battery cover and don't forget the o ring.