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Matt, Engineer
Category: Car
Satisfied Customers: 20389
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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I drive a 2005 landrover discovery 3 the 4.0l petrol...restart

Resolved Question:

I drive a 2005 landrover discovery 3 the 4.0l petrol. If i have been driving for a while the battery light goes on and there seems to be less electricity running through the car, sometimes the battery light goes of by itself and everything is fine. If i restart the car the light is off again. Could this be as simple as changing the battery or is it the alternator?
Submitted: 4 years ago.
Category: Car
Expert:  Matt replied 4 years ago.

1st 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

And one last thing is – how old is the battery? – As even good quality ones need replacing every 5 years and faulty battery just won’t hold a charge
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