Rather than play a guessing game with voltages I would start by taking resistance readings and see what goes with what. Also, many UPS transformers use multiple tap transformers so they can be used globally (120V & 240V systems). Many UPS units, depending on size and ratings use not one but a pair of 12V 7AH batteries in series, so they run on 24 VDC and not 12 VDC. The charging circuits start with 12V-0V-12V. Anyway, I would start using an ohm meter and see what goes with what, also if possible note the wire gauges where the leads exit the transformer windings.
Ron