Old 1996 Motherboard 3KVA APC UPS Shuts Down and Enters Sleep Mode on Battery Power

[Likhon]

​Hello everyone,
​I am facing a critical issue with my old APC 3KVA UPS (equipped with a 1996 motherboard version).
​The exact problem is described below:
​When the UPS runs on regular grid power (AC line), it works completely fine and smooth without any issues.
​However, as soon as it switches to battery mode during a power outage, exactly 4 to 5 minutes later, all load section lights and battery section lights start blinking together, and the UPS automatically goes into a sleep/shutdown mode (cuts off output power).
​If grid power returns within those 4 to 5 minutes, the UPS keeps running on battery for that exact duration, then shuts down anyway even though grid power is already back, and finally restarts to switch back to the grid.
​Could you please guide me on what might be causing this 4-5 minute timer-based shutdown behavior on this 1996 model and how to fix it?
​Thank you in advance for your support!

[Teken]

What is the exact APC UPS SKU? Provide a photo of the front and back of the unit.

In the interim, connect the system to a computer running APC Power Chute Software.

Perform the same tests while PCBE / PCSS is connected to the target UPS. Provide the logs from Power Chute for review following this APC FAQ:

https://www.se.com/us/en/faqs/FA159672/

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