Battery post (3/8 bolt type) turns in battery.

what ever you do be careful that is a exploding battery just waiting to happen if you have the other cable still hooked up. if it sparks inside while you are trying to turn it BOOM! where a face shield and hold the cable in place to see if it will loosen. if not cut the cable and replace cable with the new batteries.

 

Yup I had that happen to me once, just had to replace battery. Like super hauler said be very careful as fumes could be escaping from
that post and any spark you will have an explosion. I've had a battery blow up in my face a couple times, very scary and was lucky, wear a face shield Vause you can't replace your eyes.

 

Try a good 1/2 impact and burp it off.
Might be just quick enough to buzz it off.
Carefully thou.

 

cut the nut off with an angle grinder. Or the whole post.

 

It's probably a cheap exide battery. Made in China.

I'd definitely wear a face shield and gloves.

 

A nut splitter works well. And that battery is toast. That stud has broken loose inside.

 

Someone suggested cutting the nut/post with a grinder. I don't know if it was sarcasm or not but please DON'T DO IT! Batteries give off hydrogen gas when they charge/discharge and one little spark could blow that battery (or the other 3) to pieces. Batteries are practically bombs and an often overlooked danger that people don't ever think of when working on vehicles.

I'd be wearing rubber gloves, safety glasses and a faceshield when around that battery. Even that post turning inside the battery could cause an arc in between the post and the plates. If you have enough slack in the cable I'd suggest cutting the cable with cable cutters right at the crimped on ring terminal. Then have a new terminal crimped on and heat shrinked to prevent moisture from getting in. As someone else suggested, a nut splitter would work too, as long as you made sure to keep the area well vented in the off chance it might cause a spark.

 

Usually an impact will spin it off, you may have to pull up on the cables a bit to get some pressure on the stud to hold it still and blip the trigger on the impact. Do NOT use a grinder to cut it, batteries can explode doing that. I had one cross threaded so bad that it would not come off, I just carefully used a small pry bar to work the stud out of the soft lead (the battery is bad anyway). Once it came out, it was easy to grab with vise grips.