I have an 89 f150 the battery had been going dead lately I checked all the cables they look good as far as I can tell this morning I started it and turned the heater on to thaw the ice off my windshield when I came back 20 minutes later the v gauge had dropped a lot plus when I went to move it I backed up stopped went to put it into drive and it almost died on me correct me if I'm wrong but my truck should still run without the battery right so if it started and the battery was dead it should not effect it when I got to work about 10 minutes later I shut it off then tried it again nothing wouldn't start any help or suggestion would be most apritiated thank you