It started months ago, maybe one every few weeks the battery would act like it had a dirty post but would spin right over when I shorted on the solenoid (69 Ford pickup) This never happened at home (heat soak?) so I always just fired it up under the hood and drove away. It started happening a bit more often and I had cleaned all my connections. So a few days ago I ran out of gas, poured in the can I was carrying and it did it again only it would crank real slow from the key or shorting on the relay. I put a volt meter on the battery and it had 12.76 but as soon as I would crank it went down to under 8 and the battery gas smell would be very noticeable. I got a jump and drove the mile home, shut it off and it cranked right up fine, alternator is charging good at 13.8. I changed the battery and so far haven't had any troubles (5 days) and yesterday I used the old battery to jump the skidsteer and it still had 12.7
I had not done a starter draw or any voltage drop test test so i don't know if that is a problem but I think the starter would poop out pretty soon if it was problematic.
Any guesses? We'll see who nailes it after I get around to pinning the problem down.