Trying to repair a crack on plastic casing on a everstart 12 volt battery after trying to connect something to the right terminal that didn't fit properly. Did some research ans decided to give JB weld a shot because from what I've read so far it's supposed to be resistant to acid and will bond to plastics, but during and after application it began to bubble up in some areas so I'm wondering if it wasn't the right thing to use? Or is the plastic the battery case is made out of not compatible with epoxy? Reasons why JB weld appears to be bubbled in some spots? Or really just any other suggestions on different methods for repair?
Epoxy is a good choice for plastic, but it won't keep the crack from expanding without some help. I find that epoxying a piece of fiberglass mesh tape across material works well in a lot of cases, if I were looking to seal a battery I'd first fill the gap with epoxy, then bridge the crack with a small piece of fiberglass mesh tape.
However, you have to be aware that it's a temporary solution - epoxy isn't acid proof, once it's leaking it will eventually eat away at any repair you do. A drip will eat through bodywork and vital components, whereas a crack could lead to a catastrophic failure of the battery. Battery acid all over your engine compartment will lead to expensive repairs, for me it's better to bite the bullet and replace the battery.
Had experience trying to repair damaged battery cases, splits, punctures etc.
Depending on the plastic, the most reliable solution was to use a soldering iron to melt the material.
The big difficulty is that the crack is all the way through, but with a compound you only touch the surface so the acid works through from behind, also, the range of temperature becomes an issue with constant cycles of thermal expansion...