klanger - the 400 Majesty uses a sealed lead-acid battery. I don't know about the 250 - it is not sold in the U.S. I don't know very much about polymer batteries, except that they are MUCH lighter than lead-acid.
When I had a Mustang (car), there was a company that made a polymer battery for it that weighed 17 pounds - the lead acid battery for the Mustang weighs 50 pounds, but the cost for the polymer battery was $175 vs. about $50 for the lead-acid battery. I had re-located my battery from the engine compartment to the trunk, over the passenger side rear tire, for more traction off the line in drag racing, so I figured a lighter battery wouldn't help.
I saw your post about taking the battery inside - we used to do this in Canada when it was really cold! Also, they sell battery warmers in Canada - a little electric blanket that goes around your car battery and plugs into an extension cord - they work. The most effective things were block heaters - electric heaters that heated the coolant in the engine, and kept the engine - and most importantly - the oil, warm. In some cities in Canada where it gets really cold - like Winnipeg - there are electric outlets at every parking place.
WITF - yes, proper charging can revive a sulfated battery - but not completely. It will reverse some, but not all of the sulfation. It's best to prevent sulfation in the first place, but like you said, a sulfated battery may be able to be fixed and work for quite a long while. You want a battery charger like yours, with a desulfation setting. When I was young and dumb (instead of old and dumb :wink: ) I left my first motorcycle in a shed over the West Virginia winter. Of course, come spring, the battery was dead and the bike wouldn't start. So I took the battery out and charged it with a big car battery charger until the acid was bubbling with hydrogen bubbles - man, I killed that thing! So it was off to the cycle shop for a new battery.
This brings up one more topic - as an ER doctor I see this a couple of times a year. When you charge a lead acid battery, hydrogen gas is given off. Folks - hydrogen mixed with the right amout of oxygen EXPLODES! That's why NASA uses liquid hydrogen as a rocket fuel.
DON'T let any ignition source get near a charging battery. What I see is people who charge a battery and check on it while smoking a cigarette - the battery explodes, and they wind up with eyes full of embedded plastic particles and battery acid. The best thing to do is wear safety glasses whenever working with a battery.