General Question - Cheap battery diagnostic tester

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Sat 3 Jan 2009 20:48
General Question - Cheap battery diagnostic tester - passat 20v se
It's that time of year again!. It would be very useful if I could check the level of battery charge on my 2003 1.8 Mondeo without having to visit a battery specialist with clever and expensive equipment. Does anyone have positive experience of the small LED battery/alternator testers that cost less than £10.00, eg Rolson, Sealey, Draper. Do they work? Even if they only give a rough guide, bearing in mind the low cost, they seem to be worth the investment.

{Made non car specific as the question *might* be handy for anyone else, but have included details of car in main post instead}

Edited by Dynamic Dave on 04/01/2009 at 01:42

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Sun 4 Jan 2009 10:53
General Question - Cheap battery diagnostic tester - astrabob
Easiest way is to measure the battery voltage with a Digital Multimeter. You can get these quite cheaply from Halfords, Screwfix, Electrical Wholesalers etc.

Make sure you have not run the car engine or charged the battery in the last 6 hours.
(If you have, switch on dipped headlights for 30 seconds only, then leave 5 minutes)

Make sure that the lights / radio etc. are all switched off.

With meter on DC volts setting, measure battery voltage.

Results are:-
Reading Charge level
12.65V 100%
12.45V 75%
12.24V 50%
12.06V 25%
11.89V 0%

To test alternator, measure battery voltage with car engine running. Should be approximately 13.2V to 14.4V. Might increase slightly if you rev the engine.

I am sure that the LED testers are based on these voltages.
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Sun 4 Jan 2009 11:31
General Question - Cheap battery diagnostic tester - jc2
And you can use the DMM to check other things,continuity,fuses and even mains voltages and they are available for the level of accuracy you want for well below £10.
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Sun 4 Jan 2009 12:04
General Question - Cheap battery diagnostic tester - piston power
You can pick up a drop tester off e bay they put a load over the battery should hold in the green for 9 secs.
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