Battery percentage is 3% but battery is full

Hello, I’m a HA 11.5 noob and setup my first sensor for temperature.
Surprisingly and conveniently, HA also shows the battery percentage which is fantastic!
However, the battery shows 3% which is wrong as I test the batteries outside of the sensor hardware and the 2 x AAA’s are full.

Any suggestions please?

What make and model is your sensor?

Is your device very cold?

Are you using NiMH rechargeable batteries?

The problem is that these sensors use a very simple voltage measurement to estimate the battery capacity. Unfortunately voltage can be affected by temperature and the battery chemistry (NiMH = 1.2V cell, Alkaline = 1.5V). Or even dirty battery contacts presenting a high resistance.

I have an Aqara temperature sensor in my freezer that shows 0% battery. It is working fine and I expect it will continue to for many months.

3 Likes

I’ve found the battery percentages to be very unreliable. I have one device which has been sitting at 11% for months now. Today it jumped to 22%. It sends data just fine. If history is any guide, it’ll go back to 11% and sit there for a few more months until it finally stops sending data. Then I’ll swap the battery. I have another one which sits for months at 100%, then rapidly falls.

I have an automation which saves all my battery values to a .csv file once a week so I can see the trends and know which ones to proactively change if I plan to be a way for a while.

1 Like

What make and model is your sensor? Tuya WiFi Zigbee Temperature Humidity Sensor Thermometer Hygrometer Smart Home

Is your device very cold? around 30 degrees Celsius

Are you using NiMH rechargeable batteries? 2 x AAAs Ni-Mh rechargeable 2000 mAh, brand name: Energy

Thanks for the info, makes sense and I’ll still use it, as the metric is still interesting.

it’s almost certainly the ni-mh batteries. standard alkaline batteries are 1.5 volts. and degrade gradually in voltage as they are used. devices have a tolerance for going somewhat below 1.5 volts (or 3.0 if you’re using 2 in series).

ni-mh chemistry has a voltage of 1.2v. it hold pretty steady at that as its used, then falls like a cliff:
image

www.stefanv.com/electronics/using_nimh/nimh_vs_alkaline.gif

so some devices that aren’t designed for nimh either won’t work if it won’t tolerate the voltage that low, or it’ll think the battery is low because think it’s further down on that red line…

1 Like