If you use an old Android phone as a shop or home security camera, it will spend most of its life on a charger. So it is easy to think the battery does not matter.
It matters the moment the power goes out. In a power cut, the phone's own battery is the only thing keeping the camera recording. In places where power cuts are a normal part of the week, the battery is the camera's backup power supply, and an old phone's battery may be much weaker than it looks.
This guide shows how to check an old phone's battery before you give it camera duty, using only what is already on the phone or free from the phone's maker. No battery app to buy, no subscription. It is written for budget and older phones, and for shops and homes where the electricity is not always there.
The short answer
Check the battery in three ways before you trust an old phone as a camera that must keep recording through a power cut:
- Ask the phone. Some phones have a built-in battery health screen. Samsung phones have a free diagnostic in the Samsung Members app. Newer Pixels have Settings → Battery → Battery health.
- Look at the phone. A swollen battery is a reason to stop, whatever any screen says.
- Time it. Unplug the phone with the camera running, and write down how long it keeps going. This is the only number that tells you what will happen in your next power cut.
The third check is the one most people skip, and it is the one that answers the real question.
Why the battery matters for a phone that is always plugged in
A phone camera on a shelf has two kinds of failure, and they need different backup plans. When the internet goes down, the phone can keep recording to its own storage. When the electricity goes down, the router usually goes dark too, so live view on your Wi-Fi stops, and the phone itself is now running on its battery. We wrote about the difference in detail in What Happens to a Phone Security Camera During a Power Cut or an Internet Outage?.
In an earlier triage list we said a battery that will not hold a charge is a weaker reason to reject a camera phone than it is for an everyday phone, because a camera phone lives on a cable (Which Faults Actually Disqualify an Old Phone From Camera Duty?). That is true where the power is steady. Where power cuts are common, it needs one more sentence: the battery decides how much of the power cut gets recorded. A phone that dies ten minutes after the lights go off will miss exactly the part you may want on video.
Check 1: Ask the phone what it thinks of its battery
On a Samsung Galaxy phone
Samsung's own support page describes a free self-check in the Samsung Members app:
- Open Samsung Members.
- Tap the Support tab.
- Tap Get Started under Phone diagnostics.
- When the test finishes, tap the Battery status icon.
Samsung lists three results. Normal means "No performance issues with the battery." Weak means the battery's efficiency may have dropped from long use or conditions. Bad means "The battery life has significantly degraded." Menu names can differ a little between app versions and countries.
On a Pixel phone
Google's Pixel help page says Settings → Battery → Battery health is available on Pixel 8a and later. It shows the battery capacity as "Normal" or "Reduced", and Google recommends replacing the battery when it is labelled Reduced. The same page says Pixel 3 through Pixel 8 Pro and Pixel Fold "should retain up to 80% capacity for about 800 charge cycles", and Pixel 8a and later for about 1000.
Most phones that end up as cameras are older than a Pixel 8a, so for many readers this menu will not be there.
On other phones
Some brands have their own service or "phone care" app with a battery test. If yours has one, use it. If it does not, there are two more options below, and the timing test in Check 3 works on every phone.
What the phone can and cannot tell you
Under every battery app, Android itself reports a small set of facts about the battery. Android's developer documentation describes a system message (ACTION_BATTERY_CHANGED) that carries the battery's level, charging state, temperature, voltage, and a health value. Because it is a "sticky" message, any app can read the latest one without special permissions. So a simple free battery-info app can show you these same facts.
The health value is one of a short list of codes, defined in Android's BatteryManager reference:
| Code | Name | What it means for a camera phone |
|---|---|---|
| 1 | BATTERY_HEALTH_UNKNOWN |
The phone is not saying. Do the timing test. |
| 2 | BATTERY_HEALTH_GOOD |
No fault reported. Not the same as "full capacity". |
| 3 | BATTERY_HEALTH_OVERHEAT |
Too hot. Move the phone, take it out of its case, check the charger. |
| 4 | BATTERY_HEALTH_DEAD |
Do not use this battery. |
| 5 | BATTERY_HEALTH_OVER_VOLTAGE |
Charging problem. Try a different charger and cable. |
| 6 | BATTERY_HEALTH_UNSPECIFIED_FAILURE |
A fault the phone cannot name. Treat it as a warning. |
| 7 | BATTERY_HEALTH_COLD |
Too cold. Rare indoors. |
The most important line in that table is the second one. "Good" means the phone sees no fault. It does not tell you how much of the original capacity is left. A tired five-year-old battery can report "Good" and still last a short time on its own.
Newer Android versions report more. Since Android 14 (API level 34), the same message can include a charge cycle count (EXTRA_CYCLE_COUNT), the number of full charge cycles the battery has done. If you have a phone on Android 14 or later and a battery app that shows a cycle count, that number is useful. On older phones it is simply not there.
If you have a computer and a USB cable
If USB debugging is already set up, the command adb shell dumpsys battery prints the same facts as text: lines such as health:, temperature: and voltage:. The health: number uses the codes in the table above. The exact lines vary between Android versions. When you are done, turn USB debugging off again, because a phone left alone on a shelf should not have a debugging door open (we explained why in our Developer options guide).
Check 2: Look at the phone
No screen can replace this check. Lay the phone flat and look along its edge. A back cover that bulges, or a screen lifting away from the frame, can mean a swollen battery. We covered what to look for at the shop counter in Buying a Second-Hand Android Phone to Use as a Shop Security Camera?, and why heat and constant charging cause it in Can You Leave an Old Android Phone Recording 24/7?.
If you see swelling, stop. Unplug the phone, do not press on it, and take it to a repair shop. A camera that needs to run every day is the wrong job for that battery.
Check 3: Time it (the test that answers the real question)
Health screens give you a label. A power cut gives you a number of minutes. The only way to know that number before the next power cut is to measure it.
- Charge the phone fully with the charger you will actually use at the camera spot.
- Set it up exactly as it will run: camera app recording, screen off, on the same Wi-Fi, in the same place. Heat and signal both change how fast a battery drains, so test where the phone will live.
- Write down the time and the battery percentage, then unplug it.
- Check every 30 minutes (from another phone if you are using live view, so you do not wake the screen), and write down the percentage each time.
- Stop the test at around 20%. You do not need to run it flat to learn the answer, and you do not want the last part of a real power cut to be the part with no video.
Now you have a real number for this phone, this app setting and this place. Compare it with how long your power cuts usually last. If the phone covers them, good. If not, you have three honest options: lower the recording quality, add a power bank or a small UPS that also keeps the router running, or replace the battery.
Repeat the test every few months. Batteries get weaker slowly, and the phone will not tell you that the number has changed.
Small habits that help a camera battery last
- Use a slow charger if you have one. A phone that only needs to stay topped up does not need a fast charger, and slower charging makes less heat.
- Keep it out of a case and out of direct sun. Heat is the main enemy of a battery that is always charging.
- Keep the screen off while recording. A lit screen adds heat and drains the battery faster in a power cut.
- If the phone has a "protect battery" or charging-limit setting, consider turning it on. It keeps the battery from sitting at 100% all day. It also means less charge in reserve when the power goes, so run the timing test again after you change it.
Summary
- On a camera phone that lives on a charger, the battery is your power-cut backup.
- Samsung: Samsung Members → Support → Phone diagnostics → Battery status (Normal / Weak / Bad). Pixel 8a and later: Settings → Battery → Battery health.
- Android's own health code "Good" means no fault, not full capacity. Cycle count is only reported on Android 14 and later.
- Swelling means stop, whatever any screen says.
- Time it. Unplug it with the camera running and measure how long it lasts. That is the number your next power cut will use.
Background Camera RemoteStream is free to install on Google Play: https://play.google.com/store/apps/details?id=com.superfunicular.digicam. It records with the screen off, keeps video on the phone with no cloud account, offers live view on your local network, and can stream to YouTube Live when you have the bandwidth. More at superfunicular.com.
Sources: Android Developers, BatteryManager API reference (developer.android.com/reference/android/os/BatteryManager); Android Developers, "Monitor the battery level and charging state" (developer.android.com/training/monitoring-device-state/battery-monitoring); Pixel Phone Help, "Understand your Pixel battery" (support.google.com/pixelphone/answer/15738128); Samsung Support, "How to check when to replace your Samsung Galaxy phone battery" (samsung.com/latin_en/support/mobile-devices/how-to-check-when-to-replace-your-samsung-galaxy-phone-battery/). Menu names change between phone models and software versions; check your own phone.
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