How do I know when to charge the PV Analyzer I-V Measurement Unit?

The PVA Measurement Unit contains an internal battery that requires charging via an AC outlet. The PV Analyzer software interface will warn the user when approximately one hour of battery life remains. The software user interface displays the Disabled alert (below the Measure Now button) when the battery is nearing the end of its charge. In this state, no measurements can be taken, and the Measurement Unit battery should be recharged.