Originally Posted by
bgroper
I'm currently having some battery troubles. Trying to diagnose.
Here are some suggestions:
Get someone to do a proper load test on your battery to see how much current it can actually deliver (these act sort of like a large 12V toaster). There are also newer battery testers that can check battery condition without putting a large load on your battery.
If your car has auto stop/start it will have a Battery Management System (BMS) which try to minimise fuel consumption by reducing the load on the alternator. As result the voltage readings you get with the engine running can be a bit confusing. Mine can vary between 12.2 and 14.8V, mostly in the 13s.
Cars without a BMS are usually around 14.4 - 14.8V when the engine is running ( can be lower if the battery is being charged)
One useful diagnosing tool is to measure the voltage (at the battery terminals):
A When the engine has been switched off for at least 6 hours - a fully charged battery EFB battery should be around 12.6 - 12.7V (AGM 12.8+), 50% charged is 12.2 - 12.25V, anything under 12V is very low charge capacity.
B When cranking the engine, anything under 10.8V is reason to be cautious and I would definitely get a load test done (unless the battery isn't fully charged, in which case get it fully charged and try again ).
NB If you have an extra negative terminal on the firewall use this one (not the battery -ve terminal) for all load tests and charging.
Last edited by gregozedobe; 26-07-2020 at 02:57 PM.
2017 MY18 Golf R 7.5 Wolfsburg wagon (boring white) delivered 21 Sep 2017, 2008 Octavia vRS wagon 2.0 TFSI 6M (bright yellow), 2006 T5 Transporter van 2.5 TDI 6M (gone but not forgotten).
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