This chart shows the discharge voltage curve for a typical Li-Ion cell at different constant current load levels. The x-axis shows the effective capacity in mA-Hours that is delivered from the pack when it is discharged from full to empty. At lighter loads, the pack can deliver more energy before reaching the end-point voltage because the internal losses are reduced. Another interesting phenomenon is seen in the high-current discharge curve at the bottom. When the high current discharge is started, the battery terminal voltage drops quickly as one might expect. But after a few minutes, the heat generated due to current flow actually causes a reduction in the internal resistance of the cell, and so the voltage actually rises for a short period of time even though the battery continues to lose capacity as it is being drained. Eventually, of course, the continued discharge of the cell will reduce the voltage down to the end point of 3.0V. While the resistance of the battery is a relatively complex parameter, and varies with age, temperature, and state of charge for a given battery, it can be approximated to a first order as an ohmic resistance. The displacement between the curves at different current levels can be used to estimate the internal resistance of the battery.