Recently after I ran it on the highway for about 30min I turned it off then had to restart it but the battery wasn't putting out enough juice. Only happens when the engine is at normal operating temps. Whenit cold it starts fine. What gives?

 

I did have similiar problem with my truck. The battery was about 4yrs old and was really weak when I had it tested. So I would say test the battery first, then check and make sure your connections are clean and tight.

 

It could also be the starter. Sometimes worn out starters work fine when cold, but drag when the temperature goes up. I have an '85 now that is doing the same thing. Battery is new and checks out good. Connections are good and clean. I am checking the starter next.

 

check engine to frame grounds. covered many times on this forum. even if tight they need to be cleaned.

 

Quicklook prolly nailed it and if that doesn't work then check the main battery ground wire itself.

 

Hi,
Quicklook2 probably nailed it alright, but you might as well clean the entire thing up right. below is a copy from a post describing the procedure
Cheers,
Popa Tim

Disconnect the battery. Clean the posts and terminals. Leave them disconnected.
Disconnect the fender solenoid and clean all the connectors.
Unscrew the fender stud (ie body ground), just in front of the battery, Sand down the fender and clean up all the connectors. Reassemble but don't forget the dielectric grease. This one can be the worst one since the other end of that stud is INSIDE the fender...
Follow the Battery negative cable down to the frame. Disassemble, sand/clean and Reassemble.
Find the Frame to engine block cable. Sand/clean and then reassemble.
Disconnect and pull the starter. Clean all the connectors there. Sand the block where the starter mates to it. Sand the starter portion of this mating surface too (This is where the starter gets its ground and no ground=no start) Reinstall the stater.
Reconnect the battery.
You'll need to reprogram your radio stations and drive the truck for 20 minutes(maybe it was 10) so the computer can relearn how to manage your engine.