I replaced a battery in APC SmartUPS by hot-swapping. While the swap was all right and didn't disturb connected computers, the "Battery failed" LED on the front face kept glowing.
I tried to use apctest from apcups package. Turned off the daemon and run self test (first changing BATTDATE in EEPROM). The test run fine but didn't clear the REPLACEBATT status or the glowing LED.
How to clear the failed battery state without powering the UPS and connected equipment down?
To clear this status one needs to run the self test using the Test button on front panel.
You have to run a valid self test for the LED to clear. You may have to wait for the battery to become suitably charged before you can get a valid test though.
There is some information here about it.