Safe Battery Voltage

[SteveyB]

It's that time of year when many of us will be leaving our cars garaged and unused for protracted periods and I was wondering about what the safe minimum voltage would be to allow the battery to get down to. I know Enoch has done an excellent video showing how to wire up for a trickle charger but is it really necessary? Mine has been unused now for 3 weeks and today the voltage reads 11.3V with ignition on.
I've never had problems with any car before but it seems some high performance cars need constant charging, my brother's Bentley GT speed and Porsches soon run down and their manuals advise on trickle charging.
Do I need to worry?

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[Mike Clark]

I would say yes.

My current weekend toy (a Caterham 7) has been fitted with an FIA master switch, otherwise the battery will be drained by the parasitic load of the immobilizer in a matter of 2 weeks (ok - so the 7 has a battery about 1/3 size of a normal one but still..)

It's especially critical as my 7 is also equipped with a Gel Battery and they hate parasitic loads even more than normal batteries.

When my Mustang arrives, I'll be fitting it with the connectors, so that I can hook it up to the Optimate float charger. I figure that for the cost of the charger (and running it) it's a lot less than the cost of a battery, if it goes flat and gets killed

Before fitting the FIA Switch, I found to my cost that your day can be somewhat spoilt when you go to get in the motor and get met with nothing when you hit the "Start" button! So it's a few quid well spent!

 

[melwff]

A fully charged battery is 12.6 volts and above. The reading of 11.3 is considered a dead battery. Keeping the battery at it's normal fully charged state will lengthen the life time of the battery.

 

[SteveyB]

Very short drive today, about 20 miles on A roads, 11.3V to start with just with ignition on but immediately I started the engine it read 14.5V and reduced to 14 after about 10 miles. When I got home and took a reading with just ignition on it was 12.1V so obviously charges up very quickly. If the dry weather continues I may get out for a longer drive and reach the aforementioned 12.6V or better.

 

[stiggy]

Cold will kill a battery quick as you like. I leave my on an Optimate conditioner - as I do with my other cars/bikes. Works a treat.

 

[SurfOrFight]

12.2 v is only 60% charged in a 12v battery and you should not allow to go below this; especially in winter as will significantly shorten life or kill battery.

Plenty of charts on battery charge state - just google.

 

[SteveS]

Pretty sure i've seen my battery in the 11s and that would have been in the height of summer. I've never had a car before that's required constant charging though i've also never had one that's had so little use.

 

[Actual]

Mustang was not driven between 19/11/2016 and 16/12/2016 (4 weeks)
Dashcam has parking mode which will shutdown when voltage drops to 11.6 Volts this is the lowest setting and usually allows a few hours of parking mode recording.
Temperature today was 9 deg C
Turned on ignition and battery voltage was 10.1 Volts
Dashboard display warned battery saving was active
Not expecting much the starter button was pressed
Engine started OK (maybe slowly)
20 minutes driving
Petrol at Tesco
Started OK
Parked at Tesco
Started OK
Parked at home
1 hour later battery voltage 11.2 Volts

 

[SurfOrFight]

I have a CTEK charger, which I highly recommend and have attached a fixed quick connector to the battery. If my car has stood for more than a week I connect and charge up to full which takes about 4 hrs.

 

[Actual]

I have a CTEK charger, which I highly recommend and have attached a fixed quick connector to the battery. If my car has stood for more than a week I connect and charge up to full which takes about 4 hrs.

Mustang is parked on the driveway and I don't want to be popping the hood and attaching to the battery terminals all the time.

As Mustang is getting very little use in the Winter months (not my new toy anymore) I will see how it goes and if I need to resort to AA to get started then so be it. If I kill the battery then I will seek out a flying lead trickle charge mod.

I'm thinking of getting something like this. https://www.amazon.co.uk/Sealey-RS1...481978605&sr=8-13&keywords=jump+start+battery but how big and how beefy is need to get a 5.0 V8 started?

Or maybe this one https://www.amazon.co.uk/Clarke-400...coding=UTF8&psc=1&refRID=1V78PXXC771HYMQRA9SJ "Ideal for easily starting petrol engines up to 6 litres... this unit has 1500amp peak power output and the 1m leads are operated by a heavy duty isolator switch, so you can safely connect them to the battery.

 

[welsh treg]

Garage Queens

 

[SurfOrFight]

Garage Queen!

Wish my GT fitted in my garage. Just full of shit and the Motorbike. Nope its sitting on the drive a little more than intended after ground looping the f*##er a week ago.

 

[SteveS]

14.8 today after sitting for 10 days...

 

[SurfOrFight]

Is that reading on the cars own voltmeter with the engine running?

Battery readings should be taken with a good auto voltmeter after car/battery has stood for an hour or so; 12.7 v is a usual max reading!

Why worry? If using car more than once in a fortnight - no problem - until it gets cold

 

[SteveS]

Remembered the discussion so took the reading from the car just after i'd started it.

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