Battery reporting far off

I know that battery reporting is off, but I have low battery notifications coming in and when the battery is checked it is near 100%. Is this the platform or the IOS app. I believe it is the platform.

keep in mind when you check a battery with say a dumb meter its not giving you a real reading as the meter carries no load.

Since that battery and others are new, and I removed the battery and installed in another sensor no problems. Then put another new battery in the original device and again no problem. A few hours later another device with a fresh battery showed 15%. That one was installed less than 2 days ago. I again took that battery and removed it and put it back in the same device and again no problems.