Need Help .. Strange Problem today

Hello,

Ok dont laugh but i have a 1976 pacer in pretty good shape. SOmething scary & odd today happened and Im not a mechanic so I am kind of clueless. Was hooping someone here could give ideas what may be wrong. I will explain exactly what happened.

Got into car.. had not started it in about 4 days. Tried to start.. chuh chug chug... and would not turn over. Turned key to off and car still did the chug chug like i was cranking it. Took key out of ignition... and STILL did the chug chug! Odd. So i get out of car.. open hood.. and the chug chug stops. Get back in car and nothing now. So I get a jump pack as I assume battery is dead. As soon as i put pack on negative.. i see a spark and a tiny smoke. Pulled it off fast. Now i happened to touch the + post and it was HOT. Felt battery... HOT. Pulled it out of car. Now heres where I went wrong. Later I went to the car.. thinking something might have miraculously changed... put a different fully charged battery in. As soon as i put positive cable on.. i knew something was wrong... like I knew when i was going to put it on something was not going to be good so I almost anticipated a problem. So I touch it and rip it right off as it sizzled... Somehow the half second of touching caused a nice gash in the POST of the battery! Its like it melted the post!

So now it sits and does nothing.. Looking for some ideas what could be doing this, what I should do and what not to do. I can take pictures if needed. A bit nervous as I dont want the thing on fire or exploding !!

Thanks Kevin