Monday, November 23, 2020

UPS Battery Backup

A UPS (Uninterruptible Power Supply) provides power from batteries during a power outage. Commonly used to ensure that devices can be safely and cleanly be powered off during an outage.

Selection criteria

  • Price - < $100
  • Reputable vendor
  • Good reviews
  • Device should provide battery backup for at least 1 hour
  • USB interface – provide performance metrics

Use case

Supply battery power for a router, modem and home automation system for 1 hour.

What size UPS do you need ?

During the research it was surprising to discover how much power (watts) these devices actually used. The numbers below are based on personal observation, device specifications and benchmarks and have been rounded up, to include some buffer as they could fluctuate, based on usage.

Device specifics

Linksys WRTAC1900 router - ~12-13 watts

Motorola Surfboard SB6183 modem- ~9 watts

Raspberry PI4 - ~ 4 watts

Initial observations

The documentation was clear and the setup was basic. Configuring the device and dashboard confirmed that the battery was at 100%. Cutting the power for the first time, all devices continued to operate as expected, however the metrics were unexpected. The battery charge immediately dropped from 100% to below 75%. Power was immediately restored to determine root cause.

UPS batter graph - drop to 70%

Customer service

Based on a chat with customer service, it was recommended to “calibrate” the UPS. This is not mentioned in the documentation, however it appears there are many similar concerns and recommendations. It appears that the correct recommendation is to ensure that the load is at 30-40% during this process. It took some effort to plug in a few other devices to generate the required load to ensure that the test was compliant with the recommendations.

UPS calibration graph data

Test results after calibration

Battery drop to to 85% after 1 minute and then to 77% after another minute. However, the battery sustained power for a full 70 minutes before power was restored.

UPS performance after calibration - graph

One last test

Even with the 20% drop in battery available during the first few minutes, the battery has provided power for more than the required 1 hour.

UPS final test results


While this device does not perform as expected, it does meet our goal. Buyer beware.

UPS device

APC Back UPS Pro BX 1000VA, 8 Outlets, AVR, LCD interface, LAM 60Hz
BX1000M-LM60 - there are no direct links for this device. While this device met our needs, we can't recommend it.