How to Tell If a Car Battery Is Shorted

by Kurt Schanaman
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A car battery is typically a lead-acid type of energy storage device, consisting of six independent cells from the negative terminal side of the battery to the positive terminal side of the battery. The energy storage for each cell is around 2 volts each, meaning that a fully-charged battery with all of the cells working properly will show a stored voltage of around 12 volts. When, after a full overnight charge, a battery volt reading indicates a total voltage of 10.5 volts or less, this is a strong indicator that a cell has gone bad or that it has a short between itself and another on either side of it. To determine whether a battery has a bad or shorted cell, provide a proper charge and to then test the battery after the charging cycle is complete.

Step 1

Disconnect the car battery, remove it from the automobile and set it next to an automotive battery charger. Connect the negative (-) charger cable to the negative (-) terminal of the battery and then connect the positive (+) charger cable to the positive (+) terminal of the battery. Plug in the charger and set it for an overnight full charge, then allow the charge to take place.

Step 2

Turn off the battery charger, then unplug it. Quickly remove the cables from the battery terminals.

Step 3

Turn on your digital multimeter and set it to measure 20 volts DC (direct current.) Touch the black test probe tip to the negative (-) terminal of the battery and then touch the red test probe tip to the positive (+) terminal of the battery. Allow a few seconds for the voltage reading to be displayed on your meter. If the voltage reads a full 12 volts or slightly more, your battery is healthy. However, if the voltage reads 10.5 volts or less, then your battery has either a bad cell or two cells shorted together.

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