Battery. Question.

Potatopete · Oct 5, 2015

Hi all.
I need to replace my battery (2001 A4 B6) and went to my local car parts shop.
Walked in, told him what I wanted, he asked the reg, ordered the battery and I picked it up a couple of hours later.

Now I don't know if he's given me the wrong battery, or the wrong one was fitted to my car last time it was changed.

The one in now is 70 Ah, 700A.
The new one is 60 Ah, 540A.

Could someone explain what these numbers mean, and whether the new battery is good enough, compared to the current one.

Also, the new battery is a slightly different size, but I think it might fit. Does anyone have the exact dimensions of the oem?

Thanks everyone. How can it be so difficult to swap a battery ??

Mike_B · Oct 6, 2015

Amps, as in 540A, is the amount of energy the battery can store. Think of a fuel tank.

Ah, an ampere hour, is the amount of energy charge in a battery that will allow one ampere of current to flow for one hour. An ampere is a unit of measurement for electricity. As an example, a 5 amp fuse will be fairly small, thin wire or metal. A 30 amp fuse will be much thicker as it will carry more current.

So - the bigger the numbers, the more oomph in your battery, and the longer that oomph will be available. In reality, sticking your reg into Halfords battery chooser thing comes up with options similar to those you described. Perhaps the 700 / 70 wasn't the original?

In terms of physical size, is the new one bigger - or smaller?

desertstorm · Oct 6, 2015

The analogy above isn't quite right. The 540 amps is the cold cranking amp capacity of the battery, and it's how much current the battery will provide instantaneously to start the engine. A car with a 3.0 TDI engine such as mine needs a big battery with a high CCA figure to turn such a big engine typically 850-900 A.
The Ah figure is like Mike said related to how long the battery will provide a certain amount of current, Cars with more electrical equipment tend to have batteries with larger Ah figures as they have more to support also they tend to have larger engines.
Depending on the type of battery and the technology it is possible to have a small Ah figure but a large CCA number.
In your case with a 2.0 petrol I would say that the 60Ah 540A battery would work but I would probably refit the 70Ah 700A item.
If you use the car on a daily basis and we don't suffer to bad a winter the the 60Ah item will probably be OK.
If the car is used for short journeys infrequently and we end up with a nice cold snowy winter the bigger battery would potentially give you less issues.
There isn't really a definitive size for any car, bigger is pretty much always better when it comes to batteries as long as the alternator will support it.

Potatopete · Oct 6, 2015

Great. Thanks Mike and Desertstorm.

The new battery is a Bosch, and I looked on their website and they list this battery as the correct one for my car, so I'm guessing the current one was an upgrade.

As for the size, it's about an inch shorter but the other dimensions are the same as the current one so it will fit.

What's the best way of removing the bolt in the centre at the front of the battery? Seems to be very awkward to get to.

desertstorm · Oct 6, 2015

Best way of removing that bolt is with a socket on an extension.

Mike B · Oct 6, 2015

Its much easier if you have some help if only to hold wires clear.Being over 6 foot I still find it difficult to reach and lift the battery and it may be easier if is a little smaller and lighter.There s/b a plate at the bottom to adjust for a shorter battery.Dont forget to clear any rubbish out of the space .I would pop out the drain grommets if they are still there

Mike_B · Oct 6, 2015

Yes, long extension. Pull back the wiring loom harness which is in that "squared-off" rubber thingie. Makes life easier. You may find the breather hose won't be the same, and won't fit the new battery. I was told not to worry about this - - and ended up with a botch involving a connector for a washer tube, because I could.

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Battery. Question.

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