Thread: Cranking battery health

To get a true state of charge (SOC) reading from a lead acid battery you need to let it sit for about half an hour after charging, then take a multimeter reading with it disconnected from any load. If you're taking a reading with your IID tool then it wont be accurate as the battery has a load on it.

Battery-state-of-charge-for-Wet-and-AGM.png

Put them back into ignition mode on the traxide and see how they separate, I've had an aux kill my main before

Originally Posted by TopEndThom

To get a true state of charge (SOC) reading from a lead acid battery you need to let it sit for about half an hour after charging, then take a multimeter reading with it disconnected from any load. If you're taking a reading with your IID tool then it wont be accurate as the battery has a load on it.

Battery-state-of-charge-for-Wet-and-AGM.png

Thanks for the chart.
I’ve got Bluetooth battery monitors on both batteries, so they should be accurate (non-loaded) readings.

Disconnect the aux then see how it goes, just replaced my main after 6-7 years and although it would charge up if it sat for a few days it would struggle. My aux was keeping it afloat but the cold weather didnt help. New exide extreme and it fires up instantly.

How’s your voltage when driving?

I noticed my alternator was on its way out by the output slowly slipping down, to about 12.8 at one point. Couldn’t properly charge the batteries with that!

Otherwise agree the optima would be my suspect…

Take a look at the SSB battery range, should you need to swap out. I have these for both starting and aux now - and subjectivity think they are better than the varta and yellow top they replaced…

Hi Ghost, have you carried out any additional testing yet?

From the graph, your alternator is fine, but after such a long drive, your batteries should have been higher at rest.

I noticed they were lower than 12.4v prier to you starting your motor.

How much diving have you done in the last few months?

Originally Posted by veebs

How’s your voltage when driving?

I noticed my alternator was on its way out by the output slowly slipping down, to about 12.8 at one point. Couldn’t properly charge the batteries with that!

Otherwise agree the optima would be my suspect…

Take a look at the SSB battery range, should you need to swap out. I have these for both starting and aux now - and subjectivity think they are better than the varta and yellow top they replaced…

My Bosch cranker just started giving up this past couple of weeks. SSB88ti on its way.

Originally Posted by drivesafe

Hi Ghost, have you carried out any additional testing yet?

From the graph, your alternator is fine, but after such a long drive, your batteries should have been higher at rest.

I noticed they were lower than 12.4v prier to you starting your motor.

How much diving have you done in the last few months?

Hi Tim

Things I’ve done:
- disconnected both batteries from each other (removed +ve lead from aux) , then had auto elec use a battery tester. Both batteries came up as “OK, needs charging”.
- been drinking most days whilst on holidays, so battery gets a bit of charge.
- been using solar panels when stationary for a few hours (& the sun’s out!) - btw thanks for taking my call and advising on charging via the Anderson plug!

But both batteries seem to settle around 12.4V after driving, and then go down overnight as the fridge runs. Both batteries will be around 12.0 - 12.1V by morning, so unless I drive or use solar, not enough charge to last another day.

The other thing I noticed is that when the car is off, and I open a door, the main battery seems to drop about 0.2-0.3V. It comes back up after a while (assuming all computers back to sleep), but always a bit lower than before opening the door - it opening the door definitely ’flattens the battery’.

Both batteries are probably 3 years old (or more?)

I’ve put a screenshot of a typical day, fridge running over night, 2 batteries isolate, you can see when we open the door on the car in the morning, then driving, fridge running etc…

any conclusions or advice greatly appreciated!!! Thanks0281FF90-BF70-4D47-A8AD-92E4F76BA210.jpg