So I installed a rebuilt alt and a new battery, took the disco (98) out for the day, came home popped the hood and the battery acid was leaking out of the covers, and was hissing by the negative post.
So I'm going to return the battery but was wondering if it could be the alt to and how I could check that, or hopefully it's just a faulty battery.
Thank you

 

Repalce the battery, if it happens again then you alt is overcharging.
The only way to check this is to have it tested.

 

Can I check the alt myself or should I take it to a shop. If a shop what shop will have the right equipment to test it.

 

Take the truck to where you bought the alternator and have it tested, sounds like it is over charging and has killed that battery.