Step 3: Connect the Battery / Batteries
Here's where you connect up the battery or batteries. Remember that the batteries are likely charged and can supply a LOT of current. I think there's another Instructable that tells how to use them for welding. You do NOT want to do any welding, so make all crimped connections before you connect them to the batteries!
If you have two batteries, make sure to cut a short piece of wire before you add the ring terminals to the other end of the wires you connected into the UPS wires in the previous step. Make sure that this jumper wire is not too short if you are putting the batteries in containers (see end of article).
Note: You might have to ream out the inside of the ring terminals if you could not find terminals with the right inside diameter.
Once you know that the ring terminals will fit, crimp them to the red and black wire ends. If you have two batteries, make the jumper with the other two ring terminals and the small piece of wire you cut off.
Connect the red wire to the positive terminal of one battery. Connect the short jumper between that battery's negative terminal and the positive terminal of the other battery. Then connect the black wire to the negative terminal of the second battery. If you do not connect them this way, you will not get any power into the UPS.