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Hi folks - I've got the 3.2 V6 with twin 6-volt batteries that have gone flat. They are just over one year old.

I'm sure the veterans among us know the joys of these f'ing batteries and you already know what I'm going to say. They have deteriorated slowly over the last 3/4 months and no longer start the car. I have a 6-volt charger that tops them up for a week or two but they drain again. I know these batteries are temperamental (likely dead) once drained, the only answer is most likely buy a new pair (sob) but before I do how would I confirm the alternator is working correctly and/or rule out other potential issues first? I've scanned with VCDS and that doesn't flag anything noteworthy but then would it anyway unless the alternator was completely dead?

Thoughts welcome - cheers!
 

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AFAIK these should be treated as a pair and charged using a 12V charger, not a 6V charger which is doing one at a time. If you can charge them so the car starts, then leave it running a couple of minutes and take a voltage check at a suitable point eg at the +12V terminal in the engine compartment, you can check the alternator this way. Or if you have an amp clamp, put it around the big alternator wire to check the current flow.
 

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Here are a few options:

1. Have a look for any manufacture date labels. If they are over 4-5 years old they could be in poor condition You say they are fairly new (confirm?), but batteries can get dead cells and faults.?
2. Start by getting the batteries fully recharged.
3. Have the fully charged batteries load tested at a battery shop, they will tell you the condition, if one or both batteries has a fault and want you to buy new batteries from them.
4. Put a digital voltmeter acoss the 12 volt connections of the series connected battery. If the battery was fully charged and has been left resting at least 1/2 hour, you should measure 12.5 to 13 volts. Or half that voltage across each battery If you measure <12 Volts and don't measure the same voltage across each battery, one battery has a dead cell. They are replaced in pairs and you should replace both together.
5. Start the car and measure the voltage again. The voltage should increase to about 14.5 volts if the alternator is charging, or half that charging voltage across each cell

If your batteries pass all the above tests, you then have to investigate parasitic current drain on the car, for which there are a few reasons. I've had a battery fail once in an airport parking lot after 2 weeks holiday away. Now I keep long jump leads in the tire well and check the battery condition and current drain at each DIY service.

I think people here are buying 'yellow tops' for the V6, but they are an unusual type and you will find them expensive.
 

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Here are a few options:

1. Have a look for any manufacture date labels. If they are over 4-5 years old they could be in poor condition You say they are fairly new (confirm?), but batteries can get dead cells and faults.?
2. Start by getting the batteries fully recharged.
3. Have the fully charged batteries load tested at a battery shop, they will tell you the condition, if one or both batteries has a fault and want you to buy new batteries from them.
4. Put a digital voltmeter acoss the 12 volt connections of the series connected battery. If the battery was fully charged and has been left resting at least 1/2 hour, you should measure 12.5 to 13 volts. Or half that voltage across each battery If you measure <12 Volts and don't measure the same voltage across each battery, one battery has a dead cell. They are replaced in pairs and you should replace both together.
5. Start the car and measure the voltage again. The voltage should increase to about 14.5 volts if the alternator is charging, or half that charging voltage across each cell

If your batteries pass all the above tests, you then have to investigate parasitic current drain on the car, for which there are a few reasons. I've had a battery fail once in an airport parking lot after 2 weeks holiday away. Now I keep long jump leads in the tire well and check the battery condition and current drain at each DIY service.

I think people here are buying 'yellow tops' for the V6, but they are an unusual type and you will find them expensive.
The Yellow Tops are outrageously expensive but the let me limp along with a parasitic drain for years since they were so powerful. When they finally wouldn’t charge, I found the red tops on Amazon.
Yellow Tops @ VW, 2ea @ $450-500, or $900-$1,000
Or
Red Tops @ Amazon.com, 2ea @ $187, or $376
Since the red tops have less juice, I’ve realized it’s critical now more than ever to chase down the drain and eliminate it for good.

Optima Batteries 8010-044 6V... https://www.amazon.com/dp/B00099HVN6?ref=ppx_pop_mob_ap_share
 

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If there's a current drain problem in the car it doesn't matter what type of batteries are fitted they both will behave the same and go flat if not charged. Many have probably put up with failing batteries and keep charging them when they are dying, but on modern cars this carries the risk of electronics system failure which could cost more to repair than the batteries.

The maximum useful life of a lead acid battery is around 4-5 years if you are lucky, but this depends on how you define 'life'. I need reliable winter starting and for me that's when my battery has to perform at its best and i don't want to burn out starter relays. If you are a Summer warm weather driver, you can run an older battery for longer. The 6V batteries in the V6 do not behave any different with some magic ingredient giving them unique long life. If you want longer life and a lighter battery, research lithium ion auto batteries.
 

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In addition to checking the voltage manually, you should be able to check the voltage and alternator load using Measuring Blocks on module 09 (Central Electronics). There may be additional information using Measuring Blocks on the gateway (module 19).
 

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AFAIK these should be treated as a pair and charged using a 12V charger, not a 6V charger which is doing one at a time. If you can charge them so the car starts, then leave it running a couple of minutes and take a voltage check at a suitable point eg at the +12V terminal in the engine compartment, you can check the alternator this way. Or if you have an amp clamp, put it around the big alternator wire to check the current flow.
True. A 12volt charger would be connected across the two batteries, so the positive of the charger would go to the positive battery post on the drivers side (left side of car) and the negative of the charger connected to the passenger side battery negative post (right side of car)

The included picture should give you an idea, its a diagram for two 12 volt batteries in series but still applicable for the two 6 volt batteries in series and a 12 volt trickle charger.
 

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I know nothing since I don't have the V6 but what little I know is the V6 has a 'Jump Start' terminal block under the hood. Of course being V.W. they were clever to realise that jump starting and battery charging on the car can introduce voltage spikes which can cause faults in electronic modules. This connection point is supposed to incorporate a filter of some kind and where I would connect a charger?

Generic diagrams whilst being correct as a schematic, do not consider the risk of charging vehicles full of electronic modules when batteries are left connected to the vehicle or the V.W addition of a filter to the engine bay terminals. It would be useful if somebody could upload a photo to show others?

There are many variables and a certain amount of luck as to whether you EOS and roof system will come back from a flat battery without module errors. If you want to be absolutely safe, disconnect one end of the battery from the vehicle before connecting the charger directly to the battery in the trunk. This shouldn't be necessary with a low current 'tender', but unless you know your charger, what it does, and the level of battery charge remaining, stay safe and disconnect one end from the car first. Second safest is to rely on V.W's spike filter (if it works?) and connect a charger to terminals inside the engine bay.
 
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