Faulty battery in UPS?

UNINTERRUPTABLE POWER SUPPLY
Batteries in the UPS typically last 3 to 5 years and it depends upon several factors. Including the number of times the unit must go on battery power and environmental conditions. There are usually several batteries in the UPS and while the battery voltage may show 13 volts, this may only be a float charge/voltage and a true indication of the battery voltage and condition requires the batteries to be tested under a load. If one battery is faulty in a set of batteries it will causes the whole battery system to fail and indicate a battery fault. A faulty charging circuit will not charge the batteries and will also cause a fault condition.

Lower powered and cheaper type UPS are switch over types, when the mains supply fails, the UPS switches over to the battery and inverter in milli-seconds which then supplies mains power to the computer and peripherals. A faulty inverter circuit and or flat batteries won?t deliver standby power when the mains supply fails.
NOTE the power waveform from these UPS is a pseudo sine wave (i.e. not a true sine wave).

The true UPS types are usually the higher KVA units (over 1500 VA) that supply continuous mains power. The mains power is connected to a charger which charges the batteries and the inverter draws power from these batteries and converts it to true sine wave mains power to the computer equipment, therefore there is no switch over time lag when the mains supply fails.