Reply With QuoteAre there any symptoms?
Against my better judgement but at my wife’s urging I bought a second hand BMW 4 series convertible a few months ago. Checking the battery using the charging points in the engine bay my Topdon 100 indicated the battery needed replacing. I booked an AA battery replacement but when he arrived (and having removed the trim to get at the battery - it’s an absolute swine to get at) - his fancy tester indicated it was a good battery. To his great credit he advised against replacing saving me me £285. Does anyone know if the Topdon can only be used directly on the battery terminals or is my unit dodgy. I know I should have asked him to try his on the engine bay charging points but I didn’t.
Are there any symptoms?
Absolutely no idea................
What type of battery is it?
What is the battery rating? (inc CCA)
Are there any symptoms of fault?
With what you have written - the most that can be offered, is a hand to hold.
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Absolutely no idea................
What type of battery is it?
What is the battery rating? (inc CCA)
Are there any symptoms of fault?
With what you have written - the most that can be offered, is a hand to hold.
I had a battery that was showing symptoms of low power - sometimes hard to start, instrument lights not good etc but when I had it tested at the service, the garage said it was good. A week later completely dead, had to get the RAC out for a new battery - ouch. Seems the tests can be wrong..
Maybe, but no evidence of that here - no symptoms mentioned.Originally Posted by vulcangascompany
Could be OP just testing on a whim and his meter showed dodgy battery (that wasn’t).
Batteries are fickle, to get a 100% accurate test i normally remove the terminals. Don’t forget a battery left for a few hours can gain a second wind and show as ok. As others have said what are the symptoms
That’s about the size of it - i assumed the battery was as old as the car and thought I’d give my tester a try. What i was trying to find out was would the reading from the battery terminal be different from the charging points in the engine bay. i would have thought they should be the same but I’m probably wrong - i usually am.
My question was : Does anyone know if the Topdon can only be used directly on the battery terminals or is my unit dodgy. I know I should have asked him to try his on the engine bay charging points but I didn’t.
99% of people would not change a near £300 battery unless the car fails to start and cant be recovered. Put your tester in the bin
Answered below, if you want an accurate battery test disconnect and go straight on the posts. The other thing to mentions is these small digital battery testers are rubbish, you normally get a wide range of results even with a good battery. If you want a proper test get yourself the old fashioned drop tester…something that actually puts the battery under a bit of strain.
Thanks - that makes sense. Although the Topdon BT100 gets excellent reviews and as well as the standard test also does a cranking and ripple test - it’s not one of those eBay plug in the lighter socket jobs.
Also remember most BMW models need the battery coding to the car, otherwise it wont work / wont charge.
has the car got stop start? does it work?
RTFM.
"Connect the RED(+) Positive battery Clamp to the (+) battery terminal, and connect the BLACK (-) Negative Battery Clamp to the Negative battery terminal."
https://cdn.shopify.com/s/files/1/05...f?v=1648192160
It is highly likely that if you connect the tester elsewhere the added impedance of the cars wiring will cause a test to fail, which is exactly what you're seeing.
I would have hoped that even a RAC roadside mechanic would have had the sense to refuse to waste his time.
These things work by testing the battery voltage under load. In doing so they are measuing the internal impedance of the battery. Car batteries are designed to deliver about 300 Amps to the starter. A good, fully charged 12V lead-acid battery will drop from about 13.8V to about 10V with a 300A-ish load. V=IR, so R=V/I : (13.8V - 10V) / 300A = 0.013 Ohms. If you test elsewhere you have to add the tiny resistance of the car's wiring to the tiny resistance of the battery and the voltage the tester sees will be much lower than the voltage at the battery.
TLDR: Test at the battery, its the only thing that works and what your tester manual explicitly tells you to do.
Thanks for the knowledgeable and comprehensive reply. You’re quite right I should have read the manual thoroughly. I guess at my age I’m not always as thorough as I should be. At least I know my tester is not crap and what to do next time.
I don’t think the AA chap would have refused to test on the engine bay charging points - he probably had 30 seconds to spare whilst he drank the coffee I made him.
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