Question about 2003 BMW Z4

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Does low voltage in ignition have to do with a weak battery

Does low voltage have to do with a weak battery

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It can do. It depends on where you are measuring the voltage. When the starter motor is turning the engine over it draws considerable current say 200 amps on a cold morning. If the battery is failing then the voltage may have dropped so low as to cause the ignition to not operate and the engine will also be turning over slower than normal. A flat battery due to leaving the interior light on overnight just requires an overnight charge. Some unscrupulous shops will just sell you a new battery.
The battery is composed of 6 cells, each of 2 volts. When a battery is old, a single cell can fail and itself become a high resistance. This resistance prevents the high current required by the starter motor from flowing yet the battery may actually measure nearly 12 volts. A high current test of the battery by an auto shop using a high current discharger with voltmeter will give a good check. Simply measuring the battery using a volt meter will tell you almost nothing, as a poor battery will still measure nearly 12 volts. A quick test at home is as follows. Turn on headlights. Get a friend to watch them as you turn the engine over by starter motor. If the lights go dim then the battery is faulty (or you have a very bad connection to the battery) Another simple check of the alternator is; with the engine idleing turn on all lights, heated rear screen etc and slowly increase the engine rev's. The lights should slightly increase in brightness as the alternator starts to charge the battery. (This check will not be visble with discharge type headlights)

Posted on Apr 01, 2014

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If the voltage drops more than is normal during the ignition cycle, this can be caused by a weak/old battery (Insufficient crank amperage) or by problems with the starter motor. Most auto part shops will test your electrical system for you for free and can determine whether the battery is having problems, the alternator is failing, or the starter motor is faulty.

Posted on Mar 28, 2014

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