I am having an interesting debate with my local dealer.

My FL2, like most, is fitted with a standard flooded cell battery (ie not an AGM).

From years of tinkering and general knowledge, I am confident that the maximum sustained charging voltage should not exceed 14.4V at normal temps (can be higher during sub-zero temps). More volts can be pumped through to stimulate gassing for an occasional recondition, but only for limited time and not frequently.

If it were AGM, that could be 14.7V, but less tolerance for over-volts.

Mine charges at 14.9V, all the time.

What does your charge at? Is it AGM or not? (If you have start/stop it will be AGM, otherwise assume it's not unless you know for sure)

my cigar lighter volt meter says 14.7 too when running Former Mod/Member, with the most post & Chicken George Arch nemesis

Which would be spot on for an AGM - do you know if you have an AGM?

(These cigar lighter meters are surprisingly accurate - mine checks out against my multi-meter)

npinks wrote:

my cigar lighter volt meter says 14.7 too when running

eBay has them.

Bill Turner wrote:

npinks wrote:

my cigar lighter volt meter says 14.7 too when running

Hi Nick where did purchase the cigar lighter volt meter from?

Cheers, Bill

I will just add that having got the car back, the voltage at the battery on a proper multi-meter is 14.73. The DROK is showing 14.9/15.0.

Couple of possible reasons - 1) car is intelligent enough to measure battery terminal volts and adjusts overall volts to achieve that - so higher at source to account for the drop in the wires to the battery (The opposite of the good old days when volts were set at the Alternator only) 2) the DROK may over-read by 100mV, but I don't think it's further out than that.

The dealer has fitted an AGM to match the charge voltage, so happy now!

Bill Turner wrote:

npinks wrote:

my cigar lighter volt meter says 14.7 too when running

Hi Nick where did purchase the cigar lighter volt meter from?

Cheers, Bill

my car is a MY14 also, Auto SD4 HSE LUX, need to check my battery

Mine is shocking at holding charge, with a dashcam running in the back ground, forever turning off

wonder if a new AGM battery would be better Former Mod/Member, with the most post & Chicken George Arch nemesis

Measure the battery 24 hours later to get a stable voltage.


Here is the starting current for the petrol engine, 238 amps


Just bought a new Varta Silver 85 Ah 800A to replace the original Exide. Still have to stick it in the car. Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 3xARB air compressors After cooler Air tank On-board OCD pressure air/water cleaning Additional 50L fuel Carpet in doors ABE 2x1kg Waeco 28L modified fridge Battery 4x26ah Solar 120w Victron MPPT 100/20 DC-DC 18amps 175amp jumper plug Awning 6x255/60R18

The voltage is fairly immaterial with intelligent charging systems and alternators, the current is what causes the damage, I suspect the current is limited to milli Amps when the battery is fully charged, there will be two circuits, the battery charging and a vehicle supply, if measuring at the cigar/ power socket then this could be a few milli volts higher than the battery voltage, but there again a cheap plug in voltmeter could well be up to 0.5 volts over or under reading. my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

There are two aspects now being discussed - charging voltage and float voltage (off the car).

The charging volts is important - over-volts will cause gassing. If the current is restricted, the volts won't rise above the expected figures.

The best and only way really to test a battery is to take off the car, charge for 24 hours, stick a 5A load for 1 minute, leave to float for 2 hours. That is your charged volts. Should be 12.7 or above. Ideally 12.8.

Then load test at C20 (Amp hour rfating /20 ) for 10 hours. Leave to float, check volts.

Can't recall the actual figures, buyt should be above about 12.5 still. Can estimate the useful capacity at this point.

Going out now, will update later.

If you are a caravan owner with a late model car which has a "Smart" alternator charging current could cause you problems.

According to Simon Barlow who runs the "Caravan Chronicles" blog under normal running conditions the alternator only generates sufficient current to keep all the car systems running and is not actually charging the battery, but under braking and off throttle situations the alternator can put out up to 18 volts which can cause damage to the caravan battery if it is connected via your 7 or 13 pin plug and socket.

For a very detailed analysis see the Caravan Chronicles blog https://caravanchronicles.com/category/electrical/

Bill T Life Honorary Member of Wallasey Motor Club.
Licenced MSA Radio Operator for 35+ years.
Rallying is the only sport.

interesting Bill, i'm sure they said my car had a smart alternator fitted when i queried the low voltage/dashcam turning off all the time, not had any issues with my caravan battery, that have become apparent, but is there a device that could be installed inline to prevent 18v hitting the caravan battery? Former Mod/Member, with the most post & Chicken George Arch nemesis

[quote="Bill Turner"]

According to Simon Barlow .... under braking and off throttle situations the alternator can put out up to 18 volts /quote]

I find this highly unlikely unless there is a fault. Under off throttle modern regen cars generate 14.7 Volts at the battery. There won't be high resistance enough to make this 18V at the charger unless there is a fault in the system.

Most caravan batteries struggle to get enough volts at the terminals to fully charge from the car. That is partly why I installed a fully regulated solar panel to ours - way way better than charging from the car or even the caravan supply (which is limited to 13.8 volts and can never charge above 80% of capacity at that level.)