However, it will not work on one that has one or more shorted cells. See the How to Test for an Unrecoverable Battery page for details on testing for a bad battery.
A dead battery is one that will not take or hold a charge. Either the charger will not turn on or the charger can be left on the battery for several days and still the battery will not provide enough power.
It takes several days to a week to revive a dead battery, depending on how far south it is.
Use The Battery Life Saver electronic device, BLS-12/24B and a good automotive battery charger. Preferably it should be a manual type with a rating of 6 to 10 amps. It is best to use an old fashioned battery charger, not one of the newer high tech Smart Battery Chargers for this purpose. Connect both The Battery Life Saver electronic device and the charger to the battery, paying attention to the polarity.
Charge the battery with BLS attached until the voltage is at least 12 volts or until fully charged. Check the voltage with the charger turned off. Use a volt meter (available from Radio Shack) or the battery tester available on this web site.
Let the BLS run without the battery charger for a period of time, 8 to 12 hours is sufficient. DO NOT LET THE VOLTAGE GO BELOW 11 VOLTS.
When the battery voltage is between 9.5 and 10 repeat step 4 then 5.
Work back and forth between 4 and 5 until the battery comes back up to operational condition.