Hot wire cutting foam-Stainless steel
I tried to use a battery charger at first and had rather dismal results. BUT, I was using a 50" bow. If you are using a 20-30" bow your results might be better. The charger wouldn't get the wire as hot as I like. Another idea is to use a model train transformer (so I am told) but the wimpy little one I tried was worse than the charger. A friend of mine used a deep cycle 12v truck battery with pretty good results. It's all a matter of amperage I guess...but I have no idea how much you really need.
The Tecoa thermal generator is simply the best way to go IMO.
Do you know anyone into model trains? The big transformers cost more than my thermal generator did.