The battery percentage calculator on the Logger is the manufacturer’s “best guess” on battery life based solely on how long the Logger has been running so, unfortunately, it’s not terribly accurate and should be used as a guide only.
We expect the battery in your Logger to last between 10 and 12 months. Various factors will affect the actual battery life, but this will be close.
New batteries are only a few dollars each and take about a minute to replace, so changing the battery is not a big deal. When you see the “battery low” notification, you should replace it straight away to keep your stock safe.