Hi, you might want to check everything else before starting work if the camera has lain unused for some years. Lens diaphragm may be sticky, no slow shutter speeds etc. If you use WD40 or similar, please don't spray it on. Spray a little into the cap and dip a screwdriver into it, place droplets where needed. I'm not familiar with US coinage but you need to find one that fits perfectly - or make a tool that does - to avoid damage. The battery box is plastic and too much force will break it.
Haven't worked on a K1000 in about 15 years but the bottom cover is held by just a few screws, 00 crosspoint driver needed. Connection wires to the battery box may also be corroded. Sometimes they can be resoldered if scraped clean but sometimes need replacement - corrosion can track right up the conductor inside the sleeve. If wires do need replacement quite a bit of dismantling is necessary.
Since everything on the K1000 works without batteries except for the meter you could just use a handheld meter if you can't fix the problem.