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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20374
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Hi do I need a new battery. I have a Nissan micra collette

Customer Question

Hi do I need a new battery. I have a Nissan micra collette 1986 D reg 1 litre 52500miles, car starts ok first time subject to a good rev, but whilst driving all my electrics seem to drain the car almost to a stand still. I had my lights on, blower on, wipers on, and phone pluged into socket. this is normally fine but today the car was losing power/drive, engine wasn't cutting out but car wouldn't go forward. Fuel gauge was falling fast too. Once I turned off all electric power he car drove fine. But even pressing the brake pedal (brake lights) seemed to affect it. Do I need a new battery or alternator etc?

Submitted: 2 years ago.
Category: Car
Expert:  Matt replied 2 years ago.

this soudns like the alternator isn't working to me

You can 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

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

then if these are OK then check the easy things like is the boot light or any other interior light staying on then check that the main battery connections are tight and in good condition also check the earth strap to the engine / gearbox. Next I'd check the current drain aspect, the best way to find what circuit is causing the excessive currant drain is to fit a current sensing multimeter in series with the positive battery lead on the car and the battery, or use a current clamp meter on the battery positive cable. A typical current drain with everything off and un-alarmed should be around 0.05Amp and if its higher than this remove a fuse and re-measure, if measurement doesn't change then replace the fuse and remove the next. Once you've isolated the circuit with the excessive drain check the wiring connections and plugs to components and the wiring harness that runs by the engine bay fuse box - the wiring harness chaffs / rubs through and gets damaged - but its not always easy to see so be careful when checking..

Customer: replied 2 years ago.



Any idea how much each scenario would cost in a local uk garage roughly obviously.


Many thanks

Expert:  Matt replied 2 years ago.
Hello Tom

if you need to have a new alternator fitted then this is about £70 in parts and an hours labour at most (typical independent garage will charge 50-£60 / hour)

a new battery is about the parts cost plus 1/2 an hours albour ( Halfords will fit it for free if you buy their battery)

and if you've got a wiring / current drain problem then parts cost will usually be pretty low (£20) but allow about 3-4 hours labour to locate the fault and repair it in this case I'd employ an auto electrician as they'll find it faster and be cheaper than a garage

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