How to Recharge the Battery for a 2000 BMW 540i
A 2000 BMW 540i alternator, as with all modern alternators, is not made to recharge a battery. It is made to maintain the current charge in a standard BMW-supplied automotive battery. When your 540i battery goes dead--and it can happen for any number of reasons such as leaving the lights on or sitting in an airport parking lot--the correct and best way to recharge the battery is by proper usage of a UL listed automotive battery charger. For safety reasons, these instructions are for automatic UL listed battery chargers only.
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Instructions
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Switch your UL listed battery charger to the "off" position, and plug the cord in to a standard three- prong electrical outlet.
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Open the hood of your BMW 540i and locate the battery.
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Connect the red or positive cable to the red or positive terminal on the BMW battery.
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Connect the black or negative cable to the car frame or engine block on the car chassis. This is the ground wire and it should never be connected to the negative terminal on the battery itself.
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Set all battery charger options to be applicable with your BMW battery. For example, if there is a 6- or 12-volt switch, set it to 12 volts. Set the amperage switch to any desired amperage that the charger allows. The higher the amperage setting, the faster the battery will charge. If there is a guide and timer switch, set the timer to the correct charging time per the included charging guide.
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Turn the battery charger to the "on" position while remaining as far away from the actual battery itself.
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Allow the battery to charge until the charging ammeter reads zero. Use that as your guide. The time to attain a full charge is dependent on battery cold cranking amps and the amperage rating of the battery charger.
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Turn off the charger when the battery is charged, then unplug it. Remove the cables in the order that they were put on, with the negative cable coming off first followed by the positive cable.
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Tips & Warnings
BMW 540i positive battery cables were recalled by the company for repair. Sparks or discharging may occur with a faulty 540i battery cable, so please see the Resources section to find out if your cable qualifies.
