UK-POLOS.NET - THE VW Polo Forum

Thanks, I agree that I should test the voltage of the battery at rest as you say (not just after switch-off). 24 hours rest is sometimes mentioned. That done periodically would help give a trend of battery health (?).

I was comparing a battery voltage (12.53) at end of trip, to the 12.2 Volts I was getting from the cigarette lighter while driving (accelerating). So the battery was not charging, but I would not think the battery voltage was itself at 12.2 at any time. So there must be a regulator/control or something else (apart from fuses) between battery terminals and consumers/cigarette socket.

Originally I was going to somehow run wires direct from battery (with fuse protection) to inside car DVM for driving test. Cigarette socket was more convenient but not always showing (I think) the voltage at actual battery terminals.

Thanks for the help you always offer, much appreciated.

You know, from my way of looking at things, checking the battery voltage some time after the car has been stopped, would only give you an idea of what the present state of charge is, and you would have to do that by having an extension lead fitted to monitor the battery voltage without wakening up any controllers that should be asleep.

Due to me having problems over battery draining issues with my daughter's late 2009 Ibiza which is now sold on and she has a brand new Leon Cupra, I ended up buying a Cetek battery tester, and that is the only type of tool I would ever use to assess the condition of a battery as it applies a test to the battery to check its Cold Cranking Current capacity, and that is a measure that can indicate how fit for use a battery still is.

I may invest in a battery tester/analyser. Seen at Amazon the Ctek (£109) and Autool BT360 (£33).

I only spent all that money because I had a serious problem, if your battery is very old and known to be dying, maybe just take a risk and spend the money on a new battery.
Don't get me wrong, having a battery tester like the CTEK one is very very handy and if you service your own cars, it allows you to perform a battery test at service time, which might save you every being let down with a failing/faulty battery.

My battery is supposed to be 'new' so really have no urgency to buy the analyser. However I like the idea of keeping track of its health to avoid surprises.

Looking also at the Topdon Artibattery 101 (£50) - gives internal resistance etc. like the others.

Also, from the test I made, I think the charging system works so I may also cancel garage booking.