As a battery discharges, the EMF may drop or the internal resistance increase; in many cases the EMF remains more or less constant during most of the discharge, with the voltage drop across the internal resistance determining the voltage supplied. Determining the charge remaining in many battery types not connected to a system that monitors battery use is not reliably possible with a voltmeter. In battery types where EMF remains approximately constant during discharge, but resistance increases, voltage across battery terminals is not a good indicator of capacity.
As a battery discharges, its electromotive force (EMF) may decrease or internal resistance rises; in many cases, the EMF stays relatively stable throughout most of the discharge process. The actual voltage supplied is determined by the drop across the internal resistance. Determining the remaining charge in some batteries without monitoring system usage is not possible with a voltmeter. In certain battery types where the EMF remains constant during discharge but internal resistance increases, the voltage at the terminals does not accurately reflect capacity.