Actually, you unplug the yellow connector and check between the 2 BLACK wires while the engine is running at high speed. There are 2 different alternators available for this Model 406777, Type 0128-E1 engine. One is a 10 amp and the other is a 16 amp. The Briggs specs call for not less than 20 VAC for the 10 amp system, and not less than 30 VAC for the 16 amp system. But, if you get less than 20 VAC, the stator is defective for sure, and if the stator is defective, both alternators use the same stator. The 16 amp alternator has bigger magnets in the flywheel, so if it needs a stator, you don't have to determine which system you have. 496458 is the part number for the stator.

The first thing i have to know is what is the K.V.A. of your U.P.S. You can run most of your stuff with 1000 K.V.A. with externally mounted batteries for hours. You can't do much with 500 K.V.A. I have my system setup that way. I took out my 18 amp batteries because they were dead. I externally mounted my 28 amp batteries because they were too big to fit in the case. As i said before i can get up to 4 hours on the U.P.S. alone. What you can do is find yourself an old car alternator with a little gas motor. Use the car alternator to keep your U.P.S. batteries up. You can go forever or until you run out of gas. You have to do a little wiring because most larger U.P.S.'s are 24 volts on the battery side. Works just fine. I loose hydro sometimes for 2 days. Always between 2 to 24 hours in the summer storms. An active U.P.S. also cleans up hydro spikes and brown outs. Give it a try and impress your friends with your wiring project. Oh yah. Depends on the age and size of the U.P.S. Some you had to use your computer to get into the rom chip and flash it telling it it has larger batteries or it will shut down on the old information of the smaller battery. I had to do that on my commercial U.P.S. when i put 1000 amp batteries in it or it would have shut down in 17 minuets under full load with the old info. It still thought it had 28 amp batteries in it.

Use your car charger to charge one battery at a time.

Chris hit it on the head. Heat is what kills batteries being recharged. What you are attempting to do is DANGEROUS. A car battery charger will sink a lot more current into that battery than it can handle. An Carbon-Zinc standard cell will cook badly. An alkaline cell may even burn. Don't even think of doing that to a NiCad/NiMH/LiOn battery unless you want to see something truly amazing (stand back and place the apparatus on a noncombustible surface). If you want a rechargeable lantern either buy one that has a rechargeable pack or one that will take rechargeable cells. I've seen a gizmo that is the size of a 6V lantern battery that takes 4 D cells. Charge using a charger designed for the type of battery you are using.