Dave,
Yes, you are drawing your battery down. You don't say what your engine rpm is when this happens. It is normal at idle. If this is happening while driving, for example high gear at 35 mph, that is not normal. If not normal then follow Bartamos's advice.
Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix