Thread: Cranking battery health

Hey ghost,

I had a cranking battery do that to me, was a super charge. Was a long time ago. The funny thing was even though it was at 12.4v resting, every tester including carbon pile had it at 1000cca. It lived a long life and got replaced when is cca eventually dropped

Hi TIm

I've been home for a few days, and managed to get the charger on the batteries on the weekend. It should 'float', to keep the charge at 100%... so we'll see how we go.

A couple of questions:
- Do you have any idea how long I should leave the charger on continously? 1 week? 2 weeks?
- And if this 'works', i assume I should see a higher resting voltage after charging (so maybe 12.6V rather than 12.4V) - is that correct?

Thanks for your help.

Rob

Hi Rob, if you follow the info in the link, it will give you all you need to know to rejuvenate both batteries.



https://www.aulro.com/afvb/the-verandah/246755-line-auto-electrical-info-8.html



BUT

Before you do the battery rejuvenation, if you can, can you carry out a simple load test on you cranking battery first?

To do the load test, have a note pad handy.

First disconnect the negative ( - ) lead on your auxiliary battery and then measure the voltage on your cranking battery and note it down.

Next, turn your ignition on, but do NOT press on the brake pedal. This will turn the ignition on without starting your motor.

Now turn your headlights on.

Go back to your cranking battery and measure the voltage every minute for 5 minutes.

After the 5 minutes, turn your headlights and ignition off.

This simple battery load test does two things.

First off it will indicate if your cranking battery is still in reasonable condition, and after a week of rejuvenation charging, it will also show if there has been some improvement in your battery’s state of charge.

With the first lot of voltages, regardless of what the actual voltage readings are, if your battery is still OK but may be in poor condition, the voltage should have dropped over the first couple of readings but should have then levelled out. You might even see a slight rise in the last voltage reading, if the battery was cold when you carried out the teat.

This would indicate the battery is still good.

If the voltage continued to drop over the full 5 minutes, it’s probable time for a new battery.

Don't forget to reconnect the negative ( - ) lead on your auxiliary battery.

Keep these voltage readings and after the week of rejuvenation charging, repeat the load test and you should see a similar voltage pattern but with higher voltage readings.


BTW, you can use your BM2 Bluetooth Battery Monitor Phone app to get the voltage measurements and take a Screen Grab of the graph while doing the test.

Originally Posted by drivesafe

Hi Rob, if you follow the info in the link, it will give you all you need to know to rejuvenate both batteries.

https://www.aulro.com/afvb/the-verandah/246755-line-auto-electrical-info-8.html

BUT

Before you do the battery rejuvenation, if you can, can you carry out a simple load test on you cranking battery first?

Hi Tim

Took the battery off charge this morning. Did the load test at lunchtime (with the Aux disconnected), as per your instructions. Seemed to remain fairly consistent over the 5mins. Data below.

I'll keep charging at night, leaving off the charger during the day over the next week, and repeat to see how we end up.

Thanks again for your insight and support - really appreciate how freely you give of your time/knowledge!

time	0	1	2	3	4	5
Main (4/8)	12.56	11.99	11.99	11.99	11.99	11.98

Batt meas 1.jpg Batt meas 2.jpg

Hi Tim

Here's an updated set of voltages...
I've had the battery on charge almost every night for 2wks (since the original measurements). I take it off charge during the day.
Looks like maybe a very slight improvement on the cranking battery?
What are your thoughts?

	0	1	2	3	4	5
Main 4/8	12.56	11.99	11.99	11.99	11.99	11.98
Main 16/8	12.67	12.05	12.04	12.01	12.03	12.02

file1.jpg file3.jpg

The constant in and out of lockdowns has slowly been killing my own battery in the D3.

Even with the USI-160 disconnected I found the parasitic drain was still too much with the battery dropping about 0.1v per day - even after several rejuvenation attempts.

I have now connected mine to a solar panel and charge controller via the rear white plug whenever the car is parked up.

Hi Ghost, sorry for the delay in replying, I'm flat out.

I think your battery is fine but it would be interesting if other D4 owners could carry out the same load test so we could compare.

This is that really relevant but here is the load test results from my Tiguan this morning.

NOTE the cranking battery is nearly 5 years old.

Tiguan Load Test 21/08/21


11:14 - 12.51v, Tiguan locked

11:15 - 12.23v, After unlocking


Ignition turned on, headlights on.


11:15 - 11.68v.

11:16 - 11,68v

11:17 - 11.65v

11:18 - 11.64v

11:19 - 11.61v

11:20 - 11.61v


Ignition and headlights turned off


11:21 - 12.08v

11:22 - 12.29v


Exited and Locked Tiguan.


11:23 - 12.20v

11:24 - 12.35v

11:25 - 12.38v


12:08 - 12.47V

Load Test 23Aug21

D4, main battery 2.5 years old, test with main and aux isolated.

0 Locked 12.78
1 Unlocked. 12.43
2 Ignition and lights. 12.03
3 “ 12.17
4 “ 12.18
5 “ 12.17
6 “ 12.16
7 “ 12.16
8. Off and locked. 12.49
9 “ 12.53
10 “ 12.55
……
30 “ 12.77