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Ecosse
Member Since: 07 Jan 2005
Location: Grampian, Scotland
Posts: 889
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Anyone know what the battery voltage should be with engine "off" and also what it should be when the engine is "on" ie the alternator is providing power?
I've had a couple of instances where the engine seems to be finding it harder to start up from cold so am wondering if the battery is in need of replacement but thought I should first check that the alternator was producing the correct voltage before spending on the battery.
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 20th Nov 2019 4:03 pm |
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Gary_P
Member Since: 03 May 2016
Location: Kent
Posts: 1516
  
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Sorry, these are engine non running voltages.
Voltages whilst engine running should be about 14.5V Gary
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Discovery 4 HSE 2016MY
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| 20th Nov 2019 6:31 pm |
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M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8057
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Voltage alone does not provide cranking torque, you need amps to crank an engine, 800+ in the case of a Discovery 3/4, although without volts you will not have amps(CCA), if you have less than 9v when cranking you will have faults appear, i.e. special programs off, clock reading —/—.
A fully charged battery should be 12.85v, half charge 12.6. It can when others can't,
It will when others won't,
It goes where others don't.
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| 20th Nov 2019 6:46 pm |
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Hardware
Member Since: 28 Jun 2016
Location: Hiding under the M60
Posts: 12694
 
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a "12 volt" lead-acid battery is actually 6 x 2.2v batteries in series, so 2.2 x 6 = 13.2v when in best condition and fully charged.
and that's maximum. any current drain lowers it but higher drains will lower it a lot and keep it low.
simplistically ...
The chemistry in the battery is such that it's trying to shove electrons out with a "push" of 13.2v and that's what gives us the current.
To charge it, you have to push electrons in and that's against the supposed 13.2 volts pushing them out ... so alternator will generate 14+ volts when it's charging the battery. being an "intelligent" alternator, when battery is charged, volts drop to around the 13v mark.
With engine off and no unexpected drain on the battery, I reckon (depending on age/condition of the battery) anything over 11.5v would be ok.
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| 20th Nov 2019 8:39 pm |
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dgarside
Member Since: 17 Jan 2010
Location: Holmfirth
Posts: 732
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Last time I checked mine when it was well charged after some long runs was 12.7v RLD CB Bracket
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| 20th Nov 2019 9:45 pm |
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highlands
Member Since: 11 Jan 2010
Location: NW Highlands
Posts: 5095
 
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Hardware wrote:a "12 volt" lead-acid battery is actually 6 x 2.2v batteries in series, so 2.2 x 6 = 13.2v when in best condition and fully charged.
Nominal open-circuit voltage is closer to 2.1V than 2.2V...much closer to 2.1V at current temps.
Hardware wrote:With engine off and no unexpected drain on the battery, I reckon (depending on age/condition of the battery) anything over 11.5v would be ok.
I'd be concerned at anything lower than 12V. I'd only expect to see 11.5V when the glow plugs are active.
Disconnected I'd want to see 12.3V or higher, preferably more like 12.5V+. Black 05 TDV6 HSE Auto
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| 21st Nov 2019 12:27 am |
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M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8057
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We have to be clear here as to when and how the battery is being checked, the figures I have given are for a disconnected battery, a connected battery will not give an accurate reading as unknown current will drawn from it.
The higher voltages over 12.85 can only be achieved with a battery charger not the alternator. It can when others can't,
It will when others won't,
It goes where others don't.
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| 21st Nov 2019 9:44 am |
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Ecosse
Member Since: 07 Jan 2005
Location: Grampian, Scotland
Posts: 889
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Thanks everyone - voltage with engine not running is 12.2v across battery terminals, then when running goes to 14.6v which I assume is the alternator charging the battery. May try a conditioner charger, but otherwise from the posts it sounds as if it's new battery time!
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| 21st Nov 2019 10:12 am |
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oggy_oggy
Member Since: 06 Apr 2019
Location: Gothenburg
Posts: 21
 
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Should the battery voltage drop significantly when vehicle is woken up?
Car sits outside, temperatures between -6 to 0 celsius
Connected to the car, in sleep mode the battery shows 12,68
When the car is woken up the voltage drops quickly to 12,5 and then creeps down to 12,35.
If i lock it up and it goes to sleep the voltage creeps back up to ~12,68 again
I have a D4 without start/stop and non AGM battery. Have gotten lots of low battery warnings this winter if i leave car unlocked for a couple of minutes. Have had it checked by independent LR specialist and no parasitic drain, good alternator and car goes to sleep in right intervals. Just to be sure I replaced the battery. Still get the odd warning, which i guess is fair since the battery shows 12.35 when vehicle is awake, before startup.
Any ideas what to check?
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| 2nd Feb 2021 9:03 am |
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M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8057
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Yes it will drop and drop even further when the start button is pressed, it will drop as low as 9v when cranking anything lower and fault lights will come on, I would suggest you fit an AGM battery and the CCF checked to be sure it is set to the correct battery.
To check the correct voltage the car need to be allowed to go to sleep which means operating the bonnet catch to trick it into thinking the bonnet is closed and the across the battery terminals with a multi-meter.
A fully charged battery should be in excess of 13v.
Other option is a 3.5amp smart charger through the tow electrics overnight and used regularly in winter. It can when others can't,
It will when others won't,
It goes where others don't.
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| 2nd Feb 2021 10:17 am |
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RogB
Member Since: 15 Jun 2018
Location: Mansfield
Posts: 1650
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I have one of those cheap and cheerful plug in digital battery monitors that goes in the accessories socket on the dash.
As long as you don't take the reading as absolute gospel and just use it as a reference guide its actually not a bad gadget for less than a tenner. If in doubt then get the battery and alternator tested properly.
mine used to show around 12.5v at rest, 11.5v on cranking and then rise quickly to around 14.5v depending on what I had switched on (heated screens, heated seats, lights etc) 2011 D4 XS 305 MY12 - gone but not forgotten
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| 2nd Feb 2021 10:23 am |
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