I’m just curious as to what the battery voltage should be reading at with just the ignition on? Thanks

On my FL2……12.2 volts……just checked…21h15 …....
Fairly new battery…..did 140 ml run yesterday……….not used today…….question answered…..??? FL2 SD4 HSE Lux Auto MY 2012— current
D2 TD5 HSE Man MY 1999 470kmls….gone 2014 ….lovely engine..chassis rotten
D1 300TDI Man MY 1996 56kmls….gone 1999…D2 much better
Wife’s FL1 1.8P MY 2001 32kmls …gone 2007…has Mini since.

Last edited by OxonPete on 23rd Feb 2025 9:40 am. Edited 1 time in total

I’m not sure if I understand the question

Are you asking

- Key on Engine off (if yes then go with what Pete wrote)

Or

- Key on Engine on (then it’s complicated)

Note: The voltage output of the battery will fluctuate based on the load and with key on engine off the load could be extremely variable. (Heated seats, Radio, Sat Nav, Bluetooth, defrost, cabin fan, radiator fan, fuel pump and more)

I would not try to measure voltage that way. Instead I would switch on the headlamp for 30 seconds or however ever long they stay on using the key fob and then check the voltage. Something like this would give a consistent measurement.


Let’s assume that Pete did not understand the question and that you were asking for key on engine on then you need to look at this chart

Click image to enlarge

I bought one of these;
https://www.amazon.co.uk/Charger-Voltmeter...mp;sr=8-10

It just sits permanently in the front 'Switched' socket and I have a readout that confirms the battery status.
Further proved this winter when my glow plugs had gone on strike but my 7yr old battery just kept turning it over.

ps. If you want to see the battery voltage when the car is off, plug it into the 'unswitched' socket.

@P.gill,

Hi Paul,
Libbydavies’ question asking about the voltage…..with the words “just the ignition “ suggested to me that that means engine off. I should have added a question mark after ‘ question answered’. I just edited post
…..!
As you correctly say with engine running voltage should be much higher…..

@ Libbydavies…..what’s the problem with your FL2…..? Or are you just inquisitive 🤨….? FL2 SD4 HSE Lux Auto MY 2012— current
D2 TD5 HSE Man MY 1999 470kmls….gone 2014 ….lovely engine..chassis rotten
D1 300TDI Man MY 1996 56kmls….gone 1999…D2 much better
Wife’s FL1 1.8P MY 2001 32kmls …gone 2007…has Mini since.

Thanks Pete, I’m just wondering as I’ve got some random electrical faults and errors on the dash that are stopping my car from running and even cranking and I’ve had a few people tell me that low voltage could be the reason so I appreciate you telling me what yours it at

Ok Libbydaviess,

I have seen lots of posts on this forum asking about battery condition & problems……
Thé FL2 ‘s can have lots of random faults due to battery not being 100%……so you need to have a good battery for ‘starters’……! Also same for a good earth connection to the starter motor……. FL2 SD4 HSE Lux Auto MY 2012— current
D2 TD5 HSE Man MY 1999 470kmls….gone 2014 ….lovely engine..chassis rotten
D1 300TDI Man MY 1996 56kmls….gone 1999…D2 much better
Wife’s FL1 1.8P MY 2001 32kmls …gone 2007…has Mini since.

Mine is saying 12.45 volts with the car fully off and 12.10 volts with the ignition on. Can’t get an engine on one as it won’t crank. Are these low?[/quote]

Actually it seems to have gotten even lower overnight somehow with nothing been used on the car. 12.25 volts now with everything off

Libbydaviess wrote:

Mine is saying 12.45 volts with the car fully off and 12.10 volts with the ignition on. Can’t get an engine on one as it won’t crank. Are these low?

If it's dropped to 12.25v overnight with with just the alarm on then it would seem you have a fairly dead cell, can you read the volts when you press the start button? I wonder if you are actually getting power to the starter, this may be your problem but if you have low voltage there may be a circuit that disallows power to starter. my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.