Battery - when to change?

[mawallace]

I've discovered on my VW Golf that there is a feature which shows you the state of the battery. This morning, as an example, it says:-

"SOC 80%"

So, a few questions:-

- what percentage is deemed to be an acceptable one before you change the battery?
- should you measure it after a car journey or first thing in the morning?

 

[IWMTom]

I've discovered on my VW Golf that there is a feature which shows you the state of the battery. This morning, as an example, it says:-

"SOC 80%"

So, a few questions:-

- what percentage is deemed to be an acceptable one before you change the battery?
- should you measure it after a car journey or first thing in the morning?

You don't need to change it until you start having problems.

 

[DV52]

I've discovered on my VW Golf that there is a feature which shows you the state of the battery. This morning, as an example, it says:-

"SOC 80%"

So, a few questions:-

- what percentage is deemed to be an acceptable one before you change the battery?
- should you measure it after a car journey or first thing in the morning?

@mawallace: Hi - you must have an older version mk7 because VW stopped including "SOC" in later model cars

My other guess (it's an observation, really) about your car is that it has what VW call "Recouperation" - or regenerative braking which turns your car's kinetic energy into electricity to charge its battery and boost efficiency.

If you think about Recouperation in terms of SOC, you will conclude that it's never possible for the car's alternator to be allowed to fully charge the battery to 100% SOC - because the car's Energy Management System (EMS) must always isolate a percentage of the battery's rated capacity as headroom to receive the regenerated energy.

So the SOC reading on a Golf mk7 (on models that permit the reading) is seldom if ever 100% and the reading 80% (which is normal even for a brand new battery) simply means that the alternator has successfully completed its job. The remaining 20% is the proportion of the battery's rated capacity that has been allocated to receiving generated energy from Recouperation.

I had an early mk7 with SOC facility from new for many years and the reading was rarely higher than 80% - regardless of battery replacement

As I have said, later model mk7s no longer permitted SOC readings - I suspect this happened because VW received too many questions like yours - no offense intended!!

Don

 

[Keehs360]

State of charge = soc

typically. After you’ve had the battery for three years, you’ll want to test it with every oil change till the battery is degraded enough to warrant a battery swap. Could take another year or two after the three year mark to determine indefinitely that a swap is needed. Unless you have a Subaru battery. Those things can barely last 2 years.

 

[jimlloyd40]

State of charge = soc

typically. After you’ve had the battery for three years, you’ll want to test it with every oil change till the battery is degraded enough to warrant a battery swap. Could take another year or two after the three year mark to determine indefinitely that a swap is needed. Unless you have a Subaru battery. Those things can barely last 2 years.

My first clue was when the Cobb Access Port told me that my voltage was too low and to hook up a battery charger to flash a tune. I know it's risky to flash without a battery charger hooked up but I hadn't needed to until that time. To set up the Access Port initially I used a charger but never needed to for a new tune.

 

[Keehs360]

My first clue was when the Cobb Access Port told me that my voltage was too low and to hook up a battery charger to flash a tune. I know it's risky to flash without a battery charger hooked up but I hadn't needed to until that time. To set up the Access Port initially I used a charger but never needed to for a new tune.

That's a solid safety feature

 

[golfdave]

The first time you know the battery is "on the way out" is usually when it lights up a load of ABS & power steering related warning lights on the dash...

If its 6yrs old or more it'll most likely be near end of life if a factory battery...but some were doing the above after 3yrs..

 

[plastermaster]

@mawallace: Hi - you must have an older version mk7 because VW stopped including "SOC" in later model cars

My other guess (it's an observation, really) about your car is that it has what VW call "Recouperation" - or regenerative braking which turns your car's kinetic energy into electricity to charge its battery and boost efficiency.

If you think about Recouperation in terms of SOC, you will conclude that it's never possible for the car's alternator to be allowed to fully charge the battery to 100% SOC - because the car's Energy Management System (EMS) must always isolate a percentage of the battery's rated capacity as headroom to receive the regenerated energy.

So the SOC reading on a Golf mk7 (on models that permit the reading) is seldom if ever 100% and the reading 80% (which is normal even for a brand new battery) simply means that the alternator has successfully completed its job. The remaining 20% is the proportion of the battery's rated capacity that has been allocated to receiving generated energy from Recouperation.

I had an early mk7 with SOC facility from new for many years and the reading was rarely higher than 80% - regardless of battery replacement

As I have said, later model mk7s no longer permitted SOC readings - I suspect this happened because VW received too many questions like yours - no offense intended!!

Don

Interesting! I posted a question a long time ago wondering why when I start going down a hill in a low gear for braking, the engine sounds like it has a variable load. It starts off with a lot of load and then it's like the load is lessened even though I am in the same gear. I am guessing the EMS decides the battery is charged. Also when this happens the car speeds up as if there is less engine braking. However, I'm not sure that the alternator could put enough load on the engine to notice it as much as I do.

 

[DV52]

Interesting! I posted a question a long time ago wondering why when I start going down a hill in a low gear for braking, the engine sounds like it has a variable load. It starts off with a lot of load and then it's like the load is lessened even though I am in the same gear. I am guessing the EMS decides the battery is charged. Also when this happens the car speeds up as if there is less engine braking. However, I'm not sure that the alternator could put enough load on the engine to notice it as much as I do.

plastermaster: Agree - I doubt that regeneration can explain your observation. On VW's mechanical car's, regeneration is a fairly simple process of raising the alternator voltage in the deceleration and braking phases. This does result in a "back-EMF (Electro Magnetic Force) that applies additional load on the motor, but it's a marginal increase compared to the engine braking force on down-hill travel

Don

 

[Ruffasguts]

Resurrecting... Out of the blue, our Golf 7 wouldn't start (powered up OK though). When I got it back home, I checked the charging voltage, around 13.3, which gelled with an earlier post re floating voltage when battery is good. With donk stopped, volts are 12.6. It then started OK.

But, when I did the SOC check (also from a earlier post), it's showing 0%. So, I have an SOC of 0%, one day of initial failed-to-start-but-came-good, good charging and battery residual volts. That battery hasn't been changed in 5 years.

Am I up for a new battery?

Thanks for any thoughts!

 

[DV52]

@Ruffasguts: hmm....... we are in the realm of supposition - which ain't a good place to be because successful fault-finding is based on hard diagnostic evidence!!

So, if the SOC level was really 0% - I would have expected that reading the dashboard would have been more than a tad difficult!! Don't get me wrong, it's not that I don't believe your observation - I'm suggesting that the SOC was telling porkies!

Also, I guess that it's possible - but it's difficult to understand how a modern EHB/AGM battery can be totally "cactus" (Aussie slang for cactus-f#cktus) one day and able to start a car the next day!! Wet-cell batteries do recover - but not normally to this degree!!

Anyhow and again accepting that anything is possible - the odd battery behavior does raise the question of battery wiring problems - maybe?

5 years is a good run for the battery!! But just to be sure and before you throw money at a new battery (EHB/AGM batteries ain't cheap) - perhaps check the basics like battery clamps, the connector for the battery monitor module on the negative battery lead and the integrity of battery earth cable.

Do you have access to a diagnostic device? If so, it would be very interesting to look at the SCAN report to find-out how the various modules in this car saw the event!!

Don

 

[Ruffasguts]

But just to be sure and before you throw money at a new battery (EHB/AGM batteries ain't cheap) - perhaps check the basics like battery clamps, the
connector for the battery monitor module on the negative battery lead and the integrity of battery earth cable.

Thanks Don, just rechecked and the SOC is definitely 0.0. . I had a look at/wiggled the cables as mentioned and they all look OK to me; they're all secure. It does have a small box hanging off the neg terminal which I assume is the BEM

The battery had dropped from 12.6 yesterday arvo to 12.3 this arvo.

I don't have any test gear so I think I'll take it to an auto-eleco.

Thanks for your help! Much appreciated.

 

[Ruffasguts]

Well... Checked the SOC again (next day ie day 3 since problem) and now it's showing 80%! Battery volts 12.2 after overnight. It's starting OK so I'll persevere with this one. RACWA's quoting $374 for a 700CCA EFB with registering, also a fee-free battery test beforehand. I'll keep that in mind.

 

[ColinStone]

I too am wondering about the battery. The current Yuasa YBX 9027 AGM is 5 1/2 years old. Car starts OK but stop start system doesn't operate as frequently as a few months ago. In addition the BM2 battery monitor/sense shows cranking voltage dropping to 8.54v - middle of the orange zone. Finally when engine off with stop start, the battery voltage drops from 12.6v to 12.0 or below pretty quickly.
I guess all indications of a failing battery??