JB Weld & Acid Battery Repair

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...

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.