Member Since: 14 Sep 2011
Location: annecy
Posts: 233
Is my new battery duff?
D4 2011 SDV6
My battery is four weeks old and when I put a multimeter across it with the engine off I read 12.3 volts but running it is 14.5v
If I put the meter between the positive and the chassis it starts at 12.3 and then slowly goes down to under 12v
Does this tell you the battery is not good? I would have expected 12.6v. IID Tool estimates the battery at 90% charge btw
thanks for any insights
8th Feb 2022 1:57 pm
DSL Keeper of the wheelie bin
Member Since: 11 May 2006
Location: Off again! :-)
Posts: 72785
If it’s a healthy battery and the alternator was putting out 14.5v then the voltage should be way higher than 12.3v, up at 12.8V or higher. Plus if the voltage drops like that then there is deffo an issue. Battery may be new but it’s could easily be faulty and shouldn’t be behaving like that.
Make sure your alternator is not draining the battery, charge the battery with a good charge then disconnect the main lead + to the alternator and check it after 12 hours or so, if its dropped below 12.5/6 then the battery is not good, if not suspect Alternator or a parasitic drain.
Flack
8th Feb 2022 2:21 pm
sceh
Member Since: 14 Sep 2011
Location: annecy
Posts: 233
DSL and Flack - thanks a lot for your words of wisdom I will do a test tomorrow after an overnight charge and if need be get another battery
8th Feb 2022 3:45 pm
sceh
Member Since: 14 Sep 2011
Location: annecy
Posts: 233
I have a lot to learn..
In car 12.3v
Disconnect negative and test the battery - 12.42 volts
Disconnect the positive and test the battery between terminals - 12.5 volts
I put it on charge and will try again in 12 hours when I am sure it is fully charged theoretically
8th Feb 2022 3:59 pm
sceh
Member Since: 14 Sep 2011
Location: annecy
Posts: 233
The battery I have is a Varta 95Ah 950A which I bought from the supermarket.
Since i don't want to make the same mistake twice, which battery make should I buy for the Disco4?
8th Feb 2022 5:04 pm
sceh
Member Since: 14 Sep 2011
Location: annecy
Posts: 233
I charged the battery with a charger for four hours and it read 12.86v this morning after a 12 hour rest.
I connect the battery in the car and read across the terminals and get 12.45v.
I have not run the engine yet to see what IID says
That about ball park figure, now leave it connected and check it after 24 hours, if its drained again either alternator or a battery drain on the car somewhere.
Flack
9th Feb 2022 10:01 am
sceh
Member Since: 14 Sep 2011
Location: annecy
Posts: 233
thanks - good job I didn't start it yet! Let you know tomorrow. Why the difference between the voltage when the battery is connected or not? Does this not imply a drain immediately?
9th Feb 2022 10:15 am
sceh
Member Since: 14 Sep 2011
Location: annecy
Posts: 233
After nearly three hours the battery in the car now reads 12.53 volts across the terminals
9th Feb 2022 11:31 am
Justme
Member Since: 09 Aug 2015
Location: Pwllheli North Wales
Posts: 104
sceh wrote:
I charged the battery with a charger for four hours and it read 12.86v this morning after a 12 hour rest.
I connect the battery in the car and read across the terminals and get 12.45v.
I have not run the engine yet to see what IID says
Is this OK in your view?
thanks
A 4 hour charge is not enough to fully recharge it. its ok as a get the car started charge but not a 100% charge.
With the resting volts you got I suspect that its capacity has drastically reduced which is why it fully charged to soon.
You really need a CCA meter.
9th Feb 2022 11:37 am
Justme
Member Since: 09 Aug 2015
Location: Pwllheli North Wales
Posts: 104
sceh wrote:
After nearly three hours the battery in the car now reads 12.53 volts across the terminals
That suggest a substantial drain.
100ah bat loosing 0.3 volts in 3 hours is equal to a drain of about 20% of capacity.
20 amps / 3 hours is a 6+amp drain. Thats a lot.
More likely the battery has dropped to a capacity of 50-60ah or less & the drain is less.
Can you get battery tested with a CCA meter?
Not a drop tester but one that ca actually test capacity compared to rating.
I charged the battery with a charger for four hours and it read 12.86v this morning after a 12 hour rest.
I connect the battery in the car and read across the terminals and get 12.45v.
sceh wrote:
After nearly three hours the battery in the car now reads 12.53 volts across the terminals
I'd suggest that although the voltage appears to have gone up, 0.08v is within tolerance for your measurements so, essentially, it hasn't changed after 3hrs.
Not evidence of any problematic drain IMHO.
9th Feb 2022 12:46 pm
sceh
Member Since: 14 Sep 2011
Location: annecy
Posts: 233
Right. Start again. One full night of charging to get 100% capacity and then I will repost the numbers.
Thanks for all the guidance so far - very helpful
9th Feb 2022 12:48 pm
Justme
Member Since: 09 Aug 2015
Location: Pwllheli North Wales
Posts: 104
Hardware wrote:
sceh wrote:
I charged the battery with a charger for four hours and it read 12.86v this morning after a 12 hour rest.
I connect the battery in the car and read across the terminals and get 12.45v.
sceh wrote:
After nearly three hours the battery in the car now reads 12.53 volts across the terminals
I'd suggest that although the voltage appears to have gone up, 0.08v is within tolerance for your measurements so, essentially, it hasn't changed after 3hrs.
Not evidence of any problematic drain IMHO.
Its gone down from 12.86 to 12.45 on connecting.
Some of that will be due to the start up on connecting it.
Then it recovered to 12.53 once start up had finished.
It should still be at 12.8 ish if the car is shut down & all doors / bonnets closed.
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