@mebaddog2002, Thank you for bring this issue up to me. I will be happy to help you with it.
The battery is measured based on the battery voltage. This method calculating the % capacity is just an estimation. I bring this up since there is possibility that you may have a bad battery. A battery that goes bad typically will drop in voltage really quickly. Therefore, it is possible that the percentage will looked like it is stuck at 100%.
Do you have any other battery to test with? I think we should start from that.
In addition, if you can enable Z2M logging to verbose for a few ours and filter the log just for this specific sensor based on its mac address. We are looking messages whether the sensor is frequently drop and rejoin the Z2M. If this happen very often, It will drain the battery. The process of rejoining consume huge amount of power. Let try to eliminate the issue. I am sorry I do not remember the exact line of the log message. It is really obvious message that Z2M print when a sensor joined back.
I want to make sure that I do not waste your time by sending you replacement if the Arrival Sensor is actually not the issue.
However, if we determine that the sensor somehow goes bad, I will send you a replacement. However, I do ask for your favor to return the bad one. This is very rare and valuable occurrence. When I want to be able to study which part of the sensor is degrade. I may be able to make improvement for future builds. It will help me and the user in our community.