1. Shutdown your UPS monitoring software.
2. Contact your UPS directly using some terminal program such as minicom with the settings 2400 8N1 (2400 baud, 8 bits, no parity, 1 stop bit). Be extremely careful what you send to your UPS as certain characters may cause it to power down or may even cause damage to the UPS.
3. Try sending to the UPS an upper case ‘Y’ (without quotes and return at the end; the same applyes to all following commands). It should respond with ‘SM’. If you fat finger the ‘Y’ and enter ‘y’ instead, no cause for alarm, you will simply get the APC copyright notice.
4. When you are sure you are properly connected send an upper case ‘D’. This will put the UPS into calibration mode, and it will drain the battery down to 25% capacity (35% for a Matrix) at which point it will go back on the mains. In doing so, it will recompute the runtime calibration.
5. (If you wish to abort the calibration, enter a second ‘D’ command.)
6. When you are done, restart your monitoring software.

Notes:

• Does not apply to voltage-signalling or dumb UPSes such as the older BackUPS models.
• In a future release of apcupsd this procedure will be replaced by a daemon operation.
• Do not run the recalibration command more than once or twice per year as discharging these kinds of batteries tends to shorten their life span.
• While recalibrating you should supply a load of about 30 to 35% but not more than 50%. You can determine the load by looking at the output of the apcaccess status command while apcupsd is running.