Last week, we had a 4-hour power outage. Since all our networking equipment is plugged in a UPS, I assumed internet will be up for at least an hour. When I check the logs though, it was only around 15 minutes. This meant the UPS battery needs replacement.

Now, I have an obsession (lol) with uptime. When I searched for a replacement, I was also thinking if it’s possible to make UPS run time longer. It turns out that it’s possible by replacing it with a larger capacity battery. But there are safety precautions.

Safety precautions

Don’t use maximum load of the UPS

Replacing the battery with a larger capacity means that the UPS will run longer than it’s designed. There’s a risk of the inverter overheating if it’s running at high load for long periods.

To prevent this, make sure that connected devices is not using more than 80{5fcd3cbc9de14e1587c4b983f08e4837fa7ae8985dc66bae235a2c5aa0d68677} of rated watts. My UPS is 300w. The devices connected are modem, router, PoE switch, and a low-power server for Omada Controller and PiHole. It totals only to 40-50 watts which is only 16{5fcd3cbc9de14e1587c4b983f08e4837fa7ae8985dc66bae235a2c5aa0d68677} of my UPS rated watts.

I did a 2-hour test running on battery. There was no notable heating with the inverter.

Use the same wire gauge to extend connectors

Larger capacity battery also means it’s bigger. It would have to be outside the UPS casing. Using thin wires will introduce a risk of it heating up and might cause fire.

I didn’t understand how to compute what’s appropriate for this, I just used the same wire gauge as the connector inside the UPS (looked like 12 AWG).

Other than that, things should be fine.

The battery included with it was 12v 4.5Ah. I replaced it with 12v 25Ah (5x more than the original battery). This should provide 4-5 hour run time in case of power loss. I then cut a hole in the side of UPS casing to pass through the wire to the battery.

It’s already installed but we haven’t had a power outage yet to actually see how it will actually perform.