A Niagara R2/G3 UNC/JACE is rebooting every 15 minutes and the standard output window indicates AC Power status failed and a "Battery test failed" gets logged as well.
TAC IA Series
I/A Series UNC, ENC or JACE chassis with Gel-cell backup battery
Marginal or failed battery or bad battery charging fuse
The UNC automatically performs a battery load test every 15 minutes. If the voltage drops below a predefined value, the battery test indicates "battery test failed". If the voltage is higher than the predefined value, the battery test indicates "battery test passed". This message is only reported once unless the detected battery condition changes.
A station alarm is generated only when the new outcome is different that the previous test. If a battery is marginal, the test may alternate between "passed" and "failed." Additionally, a bad or marginal battery has been known to cause random UNC reboots.
Begin troubleshooting by checking the battery fuse (field replaceable only in the UNC-500/510 controllers), connections and voltage level. If the battery voltage is low (less than 12 Vdc), disconnect the battery and monitor the UNC for errors or rebooting. If the errors or rebooting stops install a new battery. After installing the new battery, measure the battery charging voltage. The voltage reading should be between 13 and 14.5 volts DC if a good battery is connected. If the installed battery is partially discharged, the charging voltage reading may be as low as 12.5 volts.
In release 2.301.522, a change was made to how embedded controllers (UNC-410 / 500 / 510 / 520) perform the backup battery test. Formerly, a "marginal" battery might result in continuous reboots. Now, the battery test is better coordinated with the AC power test. This prevents the scenario of repeated AC power fail shutdowns upon boot up if the battery is bad or weak.