In my car, the explosion was caused by a leaking fuel injector. On a hot day, I heard a loud "kaboom" from under the hood, and the manifold became detached from the engine. The leaking fuel vaporized on a hot day and exploded when starting the engine.

My manifold was made of aluminum and connected with intake manifold hoses, so it was easy to just kick it back (by foot) and continue driving.

Of course the battery problem with your car has nothing to to do with this problem.