I've had some success (not always though) by heating a wallpaper scraper with a blow lamp and gently pushing it down the insides of the case. It melts the pitch. Ron
I drilled a line all the way around the top, away from the edges of the case. Then with some wire cutters and long nosed pliers I slowly nibbled away at it. The lead plates fell apart and soon pulled out leaving the bakalite sections. Don't go too near the case wall and break a small bit at a time. It took a while and I had to walk away from it a couple of times to not get impatient and break off too much. Patients is the answer, you only need enough out to fit a small battery.
This works for me: I find that pulling each cell's plate stack individually helps; don't try to remove all three cells at one go.
First start by removing the cell caps and then using a propane blowtorch with a fine flame, play the torch over the top of the cells until the pitch runs and exposes the cell plate connectors. Use the torch to melt through the lead connector running from each terminal cell to the center cell.
With the cell connectors exposed and severed, use the torch flame to soften the pitch around the top edge of one of the terminal end cells. With the pitch softened, use pliers to rock and pull on the cell's terminal end. The use of a thin blade scraper to gently pry into the pitch along the case edges and the cell stack top helps....careful when prying, as the case is brittle....take your time.
This is a process that takes several cycles of heating, prying and pulling, but eventually the cell's plate stack will pull free from the case.
Repeat with the other end cell, then attack the center cell.
Hazardous stuff, this and I am sure that I have shaved off a few IQ points that I could ill-afford to lose in the process.
IF you are talking about removing the top of the battery this is the way we did it at the factory in the 70's.
The battery is hung up by the terminals and a gas ( towns gas ) torch was played over the perimeter of the battery.
About 3 -4 minutes in most cases and the case drops off leaving the plates & top still suspended.
While still hot the lip was scraped to clean off most of the pitch.
