Just like the removable glow-plugs, these operate around 1.2 - 2.0 Volt. Your 12V field battery will fry it (literaly) faster than you can say OOPS. I single sub-C sized NiCd will provide over a dozen starts between charges. These days, if you buy a model with these engines, it comes with a battery case which holds 2 D-size Alcalines (in parallel).

How much current? I don't know, but I would guess a regulator which can handle 2-5 Amps should do. The glow plug will only draw as much as it needs, but the regulator has to be able to handle it without burning up.