The Battery Report

A flat low-battery threshold is great for catching alkaline AA batteries. It is almost completely useless for the lithium coin cells powering half your smart home. Device Sentinel watches both.

This report exists to answer the question your dashboard percentages cannot: Which of these cells is actually about to die?

Why You Need This

Raw battery percentages lie, especially when it comes to lithium coin cells.

Imagine waking up and seeing your front door sensor at 24% and a water leak sensor at 82%. You'd probably buy AAA batteries for the door and ignore the leak sensor. But by evening, the leak sensor is dead, while the door sensor keeps chugging along at 24%.

Here is why: the door sensor uses alkaline batteries, which drain at a steady, honest rate. The leak sensor uses a lithium CR2032 coin cell. Lithium batteries hold a near-perfect charge for months, then plunge off a cliff from 90% to zero in a matter of days. If you only watch for a flat threshold, you will miss that cliff-edge completely.

That is why Device Sentinel tracks the rate of decay. Both the threshold and the warning horizon are set on the Low Battery screen, so you are notified about the drop before the device dies.

How to Read It

The battery report is an HTML page written to your configuration folder every day.

You do not need to dig through your files to read it. Drop a standard Home Assistant Webpage card onto your dashboard and point it at /local/device_sentinel/battery_report.html. It will always display today's most current data.

The report breaks your battery fleet down into six clear sections:

1. The Bank

A clean bar chart grouping your entire readable fleet into ten-point percentage bands. It lets you see the overall health of your house at a single glance. A healthy fleet is lopsided, with a massive spike at the top and a thin tail below.

2. Falling (The One That Matters)

This section shows the cells that are measurably losing charge, sorted by an estimate of the time they have left. Each row displays the current level, its rate of decay, and the estimated timeframe until empty.

Read this as a ranking, not a precise date. Time estimates are deliberately vague ("about 2 weeks") because a cell can hold its charge for months and then drop in days. What this table reliably tells you is which cell to buy first.

3. Under the Threshold

The cells that have already crossed your flat low-battery threshold. These are the exact same devices currently warning you on your problem list and daily brief, gathered here so this page holds the complete picture.

4. Steady

All cells currently above the threshold and holding their charge. These are the batteries doing exactly what they are supposed to do. They require zero attention right now.

5. Unreadable

Any device reporting a garbage level, such as 196 percent.

6. No Battery Reported

Some devices are mains-powered and simply do not contain a battery. For other devices, the battery entity might be disabled in Home Assistant. This list helps you quickly spot sensors whose battery entities you need to turn on via the device page.