Cranking battery State of Charge test feedback

[drivesafe]

Just as a point of interest, if you folks have the time, and a digital multi meter, can you measure the voltage of your cranking battery, at the battery terminals, to see what they are being charged to.

Please allow at least 12 hours from the last time the motor was on, as this allows the battery to settle to close to it’s actual SoC voltage level.

Note, this is a request for both those who have my dual battery systems fitted and those who do not.

If you are interested in participating in this data gathering, please post up how often you use your vehicle and how long you drive for when you do drive.

It would be interesting to get some independent feedback, to see what the real SoC of cranking batteries are.

Thanks in advance, Tim.


EDIT, this chart will help with SoC readings.

[winaje]

2009 D3, Varta 950A battery, 13 hours since last run, 45mins/16km daily,each way to work, some weekend running around.
12.07v (~50%SOC?)
Hope there's no issue with the battery... Interestingly, the Optima D34 that has never been used or connected to a charger is sitting at 12.61v. Will be installing Traxide kit with USI-160 very soon, so will check again on SOC of main battery after that's done, and the car has sat overnight.

[Geedublya]

2010 D4 V8 driven 13 hours ago for 40 min/25km, this is my normal daily commute. Traxide SC80 connecting the second battery.

Varta G14 - 12.13V

Otima D34 - 12.03V - has an engel 40l on it

[p38arover]

Tim, do you want the second battery disconnected? I ask because won't both batteries show the same voltage if connected?

With my dual battery system (I have yours, BTW), the batteries are significantly different in age. Also, my starting battery has flattened a few times from the car not being used.

When I get out of bed, I'll go and measure mine.

[loanrangie]

Ron, they should be electrically isolated when not on ignition so i would'nt think it would matter ?

[p38arover]

Tim,

My Rangie gets little use so the battery mainly gets charged by an external automatic charger. I just returned from 7 weeks away to find the starting battery dead flat and neither of my multi-stage chargers would even attempt to charge. While I was away I had an auto charger attached but there was a black-out a week after I left and the charger won't restart charging, it has to be manually selected. A dumb charger got enough into the battery for the multi-stage to accept the battery wasn't shorted.

Anyway, today's measurements, the car hadn't been driven for over 16 hours.

Initial voltages after unlocking car and opening doors to get out a multimeter

Dual batteries connected:
Starting battery 12.33 volts
Second battery (in rear loadspace but measured at the front of the car at the SC40 dual battery controller plug) 12.38 volts

Batteries disconnected:
Starting battery 12.39 volts
Second battery 12.45 volts

However, both terminal voltages drifted slowly higher. after a couple of minutes:
Starting battery 12.42 volts
Second battery 12.50 volts

I didn't wait around to see if they went higher. The second battery is just a normal N70 car battery.

[p38arover]

Ron, they should be electrically isolated when not on ignition so i would'nt think it would matter ?

Not with the Traxide SC40 dual battery controller. The batteries disconnect when the main battery voltage drops below a certain point. The description here http://www.traxide.com.au/isolators/...-standard.html for the SC80 applies to the SC40.

[drivesafe]

Initial voltages after unlocking car and opening doors to get out a multimeter

Dual batteries connected:
Starting battery 12.33 volts
Second battery (in rear loadspace but measured at the front of the car at the SC40 dual battery controller plug) 12.38 volts

Batteries disconnected:
Starting battery 12.39 volts
Second battery 12.45 volts

However, both terminal voltages drifted slowly higher. after a couple of minutes:
Starting battery 12.42 volts
Second battery 12.50 volts

I didn't wait around to see if they went higher. The second battery is just a normal N70 car battery.

Hi Ron and it always looks a bit strange when you measure a battery that has been sitting for a while and when you put a small load on it, the battery voltage slowly rises slightly.

This is actually quite normal and as you opened your doors, the interior light would be a small enough load to start the chemical reaction in the battery, and this is why there is a slight rise in voltage.

[Spel1]

Tim:

Two batteries, one of your USI 160's
Constant driving for work, about 120km yesterday on Fwy.
New alternator. All recently cleaned and/or replace earth cabling.
Not much to draw, but I did have the doors open a few times last night. Might check again tomorrow to see if its different by leaving the bonnet unlatched etc.

12+ hours (overnight)

Cranking battery. Near new Optima Blue 12.33V
Second Battery. Year old deep cylcle AGM 12.33V

The digital voltmeter inside (connected to cranking batt) read 12.5 after I opened the doors and turned ign to the first postion. When I have compared the inside meter to a multimeter previously they were very close.

[TonyC]

Hi Tim,
95 Defender 130 300Tdi.

Has been sitting for approx. 2 weeks, but yesterday, started and stopped 8-10 times with run times between 1 and 10 minutes between idle and fast idle.

Cranking battery Supper Charge N70 something 12.55V 90+%
Second battery N70 case deep cycle 12.79V 100+%

The isolator is an ignition triggered solenoid.

Well be doing some decent runs next week, I'll get some more numbers for you.

Tony