Frequently Asked Question
You need to be carefull to avoid misinterpreting the reading. Typically in line mode UPS will apply charging voltage (approx 13.7VDC per battery) to the battery and boost the battery voltage to this value. When software is reading the battery voltage, it is actually reading the charger voltage. To avoid this bias you need to swtich to battery mode (simulate the mains failure). Without AC input, charger will switch off and the battery voltage will shortly stabilize at its real voltage.
Unfortunately if the battery is in very bad shape it may immediately switch off the UPS. For example UPS with weak battery is plugged to AC input, the battery voltage is boosted above minimum level and the UPS turns on. When the AC input is disconnected, the internal charger is turned off and battery voltage immediately drops below the minimum level and cannot hold the UPS on anymore. You may experience immediate shutdown. If the software was monitoring the UPS, it might have recorded one entry with very low voltage before shutdown.