Check out the fact that the scanner has parameters that you can set on how low of a percentage the battery will go before being warned.
Once you get the alert that your battery is low and you are warned, you can turn it off and turn it back on again and it will run for a bit before getting the warning again.
The default that it is set on, works fine, battery has no memory, you can keep it charged full all the time if you want or just swap out batteries from an external charger.