Battery issues and Auto Stop/Start not working

[nta16]

@Nirrain I'm all for the slower 2-amp charging and have personally found the higher 10 or 12 amp chargers more likely to kill a battery that is in a very low state.

 

Yeah time is a key ingredient but I do wonder about these less expensive "smart" and multi-stage chargers I don't think they're necessarily smart enough to sort some batteries in certain states out and you have to fool or cheat them (in true VW fashion) often to even start the charging.  I see the chargers as more for use of top ups and preventative charging more than reviving batteries that are very low.

 

If you still can(?) on a 2018 what about trying disconnecting the start/stop bit at the negative post and running the car without it.

 

Otherwise as you've put if the car's not used a lot more recharging or trickle charging or disconnect the battery (as long as it does not freeze up). - https://www.rac.co.uk/drive/advice/know-how/car-battery-conditioners-and-trickle-chargers-everything-you-need-to-know/

 

[BigEjit]

On 03/02/2023 at 14:07, RIncewindwiz said:

I did ask yuasa in my discussion with them about the state of my battery. They said

"With regards to charging, our normal suggestion would be 1/10^th of the label rating for general recharging. If the voltage is sufficient, you will charge a battery even if the current is lower, it would just take longer to do so.  To much current is not recommended as this can cause thermal issues inside the battery if used too frequently. "

So it seems that 7A not that critical and 8A, if not used too often, will be fine

 

Exactly this^^^^

 

Batteries are dumb organic lumps that need to be maintained as close to 12.72v (12.8v AGM) open circuit voltage as possible and used regularly to avoid performance decay.

The only key factor is that AGM batteries need to be charged with a limited voltage of 15v. Too much current, overcharging or rapid charging of any 12v lead acid battery will cause moisture loss through 'splitting' of the water content into oxygen and hydrogen gas. Do this too much and the moisture content loss will lead to a spark between dry spots on the plates igniting the gas in the space above. This does happen on batteries that are repeatedly deep discharged and recharged fairly quickly and frequently. AGM retain all the moisture in the glass mats, EFB and standard SLI batteries are wet flooded with far more electrolyte content.

 

If a battery is discharged towards 12v, sulphates start forming straight away. (Cant be helped, its what happens) They are reabsorbed when the battery is recharged. If they are left to harden by not fully recharging within a week or so or the battery is deep discharged, the sulphate crystals rob a little capacity from the battery by taking up/destroying some of the active material in the plates and won't dissolve back into the electrolyte. Keeping the battery in a low state of charge reinforces this until the crystals grow into the adjacent plate and create a permanent short circuit cell killing the battery or the storage capacity has been destroyed so much the battery can't hold enough energy to spin the starter and supply the vehicle systems at the same time.

 

Low mileage vehicles (7k kms/year is low!) typically kill off batteries in this way. Short trips won't fully charge a battery and the Cold Cranking Amps (CCA)/storage capacity just gets progressively lower and lower. Even the odd longer trip won't be enough to help the battery recover. Voltage can be fine initially but drops off really quickly with any reasonable current draw applied. As a guide from 12.0v, chargers need to be left in place for 24 hours to reach 12.72v or higher and achieve full saturation of the plates. AGM's will reach and hold 13v fully charged.

 

When recharging, the battery is fine if it is still cool to the touch or its not venting sulphurous gas which you can smell. In the factories as a comparison, they rapid charge them several times whilst sitting in cooling baths and the air has a lingering eggy smell. Smart chargers are set to control the charge rates for home use appropriate to the battery performance and type.