Caution: only a skilled technician should perform this procedure. BatteryWholesale.com accepts no responsibility for damage that may occur to your unit or batteries.

Note: these are general instructions on how to determine if your batteries are no longer performing or the charger in the UPS unit is not working. Testing is performed on a running unit with 120 volts of electricity. Use caution.

Definitions:
Nominal Voltage: voltage of a fully charged cell when delivering rated current
Measured Voltage: as shown on the voltage meter
Note: simply attaching the voltage meter probes to the battery terminals and measuring that voltage will NOT give you a true voltage measure. The battery voltage must be measured while the battery has load applied. For example, a 12v battery will measure 12.5v on the meter with no load applied. The same battery may measure 10.5v when load is applied. This is often the case with batteries that are bad.
Series Connection: arrangement of cells in a battery configured by connecting the positive terminal of each successive cell to the negative terminal of the next adjacent cell so that their voltages are cumulative. In many UPS back up devices, batteries are set into strings. Connectors (wire or fuse blocks) are used to connect the batteries together to form a set, which has a higher voltage or amperage than the individual batteries. For example, the APC SmartUPS 1250 uses (2) 12v 17ah batteries set in series to produce a set that measures 24v 17ah.

Procedure for testing a generic UPS (using the APC Smartups 1250 as example):
Tools needed: screwdriver and voltage meter
PLEASE NOTE: Work quickly. Do not leave the load running off the batteries. Doing so may cause them to fail.
To test the batteries: with the UPS plugged into the wall circuit and turned on, determine if the unit is charging the battery at the proper voltage. Now, unplug the UPS. The load should be running off the batteries. Measure the voltage of the batteries. This will determine if the batteries are maintaining a charge.

1. Open case. Position the battery terminals in a way that allows you to safely connect the voltage meter probes.
2. Plug the UPS into the wall circuit
   
3. Plug load into the UPS (lamp or monitor will work well)
   
4. Turn the UPS on
   Example:
   The SmartUps 1250 contains (2) 12v batteries. Measure the voltage across the pair of batteries. The measurement should be 27 – 27.5 volts; the voltage the charger should be generating. If the voltage shows less than 27v, the charger is not charging the batteries properly.
5. Disconnect the UPS from the wall.
   
6. Measure the voltage across the batteries.
   The voltage should drop quickly, stabilize, and drop slowly again (depending on the size of the load). In our example, the voltage should measure higher than 25.5 – 26 volts. If the voltage drops right away to below 23v, the batteries are not charging (or not holding a charge). Should the charger put out 27v (as described in the previous measurement) it is possible that at least one battery is not holding a charge. Each battery should measure higher than 12.5 – 13v.