Subjecting a discharged cell to a current in the direction which tends to discharge it further, rather than charge it, is called reverse charging; this damages cells. Reverse charging can occur under a number of circumstances, the two most common being:

When a hp pavilion dv7 battery or cell is connected to a charging circuit the wrong way around.

When a battery made of several cells connected in series is deeply discharged.

When one cell completely discharges ahead of the rest, the remaining cells will force the current through the discharged cell. Instead of supplying a forward voltage to the load, the discharged cell becomes part of the load and presents a reverse voltage to the rest of the circuit. This is known as "cell reversal", and can happen even to a weak cell that is not fully discharged. If the battery drain current is high enough, the weak cell's internal resistance can create a reverse voltage that is greater than the cell's remaining internal forward voltage. This results in the reversal of the weak cell's polarity while the current is flowing through the cells."Pushing" current through a discharged cell causes undesirable and irreversible chemical reactions to occur, resulting in permanent damage to the cell. The higher the required discharge rate of the hp pavilion dv7 battery , the better matched the cells should be, both in kind of cell and state of charge, in order to reduce the chances of one cell completely discharging before the others. Also, many battery-operated devices have a low-voltage cutoff that prevents deep discharges from occurring that might cause cell reversal.

In critical applications using Ni-Cad batteries, such as in aircraft, each cell is individually discharged by connecting a load clip across the terminals of each cell, thereby avoiding cell reversal, then charging the cells in series.

Depth of discharge

Depth of discharge (DOD) is normally stated as a percentage of the nominal ampere-hour capacity; 0% DOD means no discharge. Seeing as the usable capacity of a battery system depends on the rate of discharge and the allowable voltage at the end of discharge, the depth of discharge must be qualified to show the way it is to be measured. Due to variations during manufacture and aging, the DOD for complete discharge incredibly hp pavillion dv4 battery Work can change over time or number of charge cycles. Generally a rechargeable hp pavilion dv7 battery system will tolerate more charge/discharge cycles if the DOD is lower on each cycle.

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