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Matt
Matt, Engineer - BEng Hons
Category: Porsche
Satisfied Customers: 20602
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Porsche 911: 99 Porche 911, battery becomes very weak after

Customer Question

99 Porche 911, battery becomes very weak after a long drive but after it cools down it crank back again. I have a year old battery that's been tested ok
Submitted: 1 year ago.
Category: Porsche
Expert:  Matt replied 1 year ago.
Hello if the battery is getting too hot then this can really drop the battery voltage - I'd check that main earth connections between battery and chassis are tight and clean and that the battery is actually being charged in the car check that the alternator is actually charging the battery in the car by taking a battery voltage reading with the engine off then another with the engine running. The 2nd reading should be higher than the 1st and climbing steadily. And also check that the alternator is secure to the engine as this provides the ground for the charging circuit and make sure that the engine / gearbox earth strap is secure and the contacts are clean and bright. if the alternator appears not to be working - take it to a electrical specialist and ask them to test it as sometimes you can replace just the diode pack and this will repair the alternator without requiring replacement
Expert:  Matt replied 1 year ago.
hi
do you still need help?