My seven year old mower won't hold enough of a charge to do one complete mowing anymore. I bought a replacement, thinking it would be easy to pop the top off and replace it. I've got the four torx screws off, but the middle two look like 3/8" bolts. It feels like I'm getting a positive fit, but they seem to turn forever and not come out. I looked at the parts diagram, hoping to pick up on the actual size, just in case it is different or metric. They seem to be missing off the parts diagram. Does anyone know the actual size, to give me a better idea of what I'm doing wrong.

Garden - Black and Decker USA - Black & Decker CM1836 36V Cordless 18-in 3-in-1 Electric...