Member Since: 10 Jul 2006
Location: Rosyth, Fife
Posts: 3005
Resting voltage of an AGM battery
Without going into too much detail, what is considered to be an acceptable resting voltage of a modern AGM battery, lets say for example after sitting for 2 or 3 days following a 100 mile run ? I am used to old lead acid batteries, whereby 12.7v was considered to be a normal fully charged resting voltage. I know AGM batteries are different, but by how much ?
Car has been checked by LR and I have been told everything is within 'operating parameters' but I feel the resting voltage figure they quote as being 'normal' is very low. I won't say anymore at this point, I just want to get the opinion of some of the forum electrical guru's first
Member Since: 10 Jul 2006
Location: Rosyth, Fife
Posts: 3005
So really there's not any difference between the lead acid and AGM batteries Mick ? I have been assured by LR that for a D4 with an AGM battery a resting voltage of between 11.9v - 12.2v is perfectly acceptable and well within 'normal operating parameters' even though I am getting low voltage error messages when using my FBH remote heating ?
Perhaps time to get it checked at another dealership ?
7th Mar 2018 9:03 pm
Dudleydisco
Member Since: 20 Jun 2014
Location: York
Posts: 853
If we assume that the current average temperature is 4.4c, then those voltages would suggest that the SoC (State of Charge) is between 25%-50%. As Flack says, that is way too low for a resting voltage. Various sources suggest that if a battery is allowed to discharge below 50%, then it is likely to damage it.
100% SoC should be 12.756v and 75% is quoted at 12.556. The higher the ambient temperature, the higher the voltages should be D4 MY14 XXV - RLD/IID BT
D4 MY13 HSE Lux - RLD/IID BT
P38 RR - Sad parting
110 - Even sadder parting
S3 88" - Still going strong after 23 years of ownership
Yes that dealership is talking out of there , 12.2 is considered flat, 12.5 is probs the min figure.
Flack
7th Mar 2018 9:40 pm
B16 KJR
Member Since: 10 Jul 2006
Location: Rosyth, Fife
Posts: 3005
Thanks guys It sounded far too low to me, but then again as I said, I don't know if the AGM batteries work in a different way to lead acid batteries with regards to voltage. I will speak to another dealership and get it booked in for them to check it out and see what they say
7th Mar 2018 9:46 pm
Dudleydisco
Member Since: 20 Jun 2014
Location: York
Posts: 853
Just for comparison-
Normal wet Pb battery at 4.4c
100%-12.606
75%-12.406
50%-12.196
25%-12.016
AGM
100%-12.756
75%-12.556
50%-12.256
25%-11.956
Hope that helps strengthen your case D4 MY14 XXV - RLD/IID BT
D4 MY13 HSE Lux - RLD/IID BT
P38 RR - Sad parting
110 - Even sadder parting
S3 88" - Still going strong after 23 years of ownership
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum
, 12.2 is considered flat, 12.5 is probs the min figure.
