Battery draining issue

[Ranga]

I have an issue with dropping voltage on my cranking battery (hence the previous posts about alternatives). It's a Supercharge 810CCA connected to a 120Ah AGM deep cycle auxiliary via a Traxide SC80. Both batteries have an isolator switch, and have been wired up according to Traxide instructions. The auxiliary isolator switch is turned off.

The cranking battery is losing voltage. There's nothing obvious drawing power. After charging it with a CTEK charger a couple of days ago, the supplier said it tested fine (no dropped cells or anything else of interest). It's dropped from 12.81 last night to 12.69 this afternoon. I'll isolate it with the switch and check again tomorrow.

Any suggestions what might be the cause?

[Blknight.aus]

probably something electrical.

which model vehicle,

[Ranga]

1995 Defender 130. You know the one ;)
probably something electrical.

which model vehicle,

[AK83]

I'm no battery expert, but dropping to 12.69v from 12.8(whatever) would seem perfectly normal to me in that time frame.

I thought 100% SoC is about the 12.7v(maybe even 12.6) level, and most batteries in very good condition will be resting in the 12.5v point.

Colder climates affect this, but as you are up that way, those values should be fair enough approximations.

[drivesafe]

Hi Ranga, as Arthur replied, having a battery settle to 12.69v over a cold night is not bad.

I would be very happy with that reading.

[Ranga]

In the last 24 hours it's dropped from 12.69V to 12.57V - is it normal to continuously drop ~0.1V per day?

[johnp38]

In the last 24 hours it's dropped from 12.69V to 12.57V - is it normal to continuously drop ~0.1V per day?

Just went outside and checked mine it is 12.69, will hopefully remember to check again b4 I start it.

[Ranga]

Dropped another 0.11V today with no use. Surely that can't be right?

[W&KO]

Dropped another 0.11V today with no use. Surely that can't be right?

Drive it around the block….that’ll fix the daily drop [emoji6]

[Ranga]

Drive it around the block….that’ll fix the daily drop [emoji6]

Probably use more volts starting it than what I would get back [tonguewink]

[Ranga]

I had it suggested to me the alternator could be the culprit due to bad diodes. Thoughts?

Can an Alternator Drain a Battery? | It Still Runs (https://itstillruns.com/can-alternator-drain-battery-7605315.html)

[drivesafe]

Hi Ranga and if it was your alternator, your battery would most likely be flattened in a an hour or so.

Have you disconnected the SC80 from your cranking battery?

[Ranga]

Have you disconnected the SC80 from your cranking battery?
No, didn't even think of that! I now understand it could be that the auxiliary is less than fully charged, and drawing from the cranker - correct? What levels/rates in the batteries does this occur?

[scarry]

No, didn't even think of that! I now understand it could be that the auxiliary is less than fully charged, and drawing from the cranker - correct? What levels/rates in the batteries does this occur?

Put a switch in the thin wire running to an earth lug from the SC80,makes isolating the batteries easy.

I always charge mine separately as they seem to charge better,particularly if both are not AGM.

[johnp38]

Just went and checked again, 12.69

It has had bonnet up for few days and no doors opened and no second battery.

I have done a couple of intermediate readings of an increase to 12.7, a drop to 12.68 and the current reading of this posting.

The variations are probably multimeter probes resistance more than anything.

I thought them battery monitoring/isolator thingys had mosfets in them sucking less than the batterys internal losses?

[drivesafe]

Just went and checked again, 12.69

It has had bonnet up for few days and no doors opened and no second battery.

I have done a couple of intermediate readings of an increase to 12.7, a drop to 12.68 and the current reading of this posting.

The variations are probably multimeter probes resistance more than anything.

Temperature differences is the most likely cause of voltages going up and down, but in the same area.

[Ranga]

It gets stranger - it was down to 12.41 this morning, and wouldn't turn over. No idea why it wouldn't start at that voltage. I reluctantly de-isolated the auxiliary and it started fine. Bad earth?

[drivesafe]

It gets stranger - it was down to 12.41 this morning, and wouldn't turn over. No idea why it wouldn't start at that voltage. I reluctantly de-isolated the auxiliary and it started fine. Bad earth?
What was the voltage while cranking?

[muddy]

have you only got a surface charge on the battery Ryan try putting say a trouble light or something with a bit of a load on battery and see if it holds voltage

if holds -- battery ok then its terminals ,wiring etc