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25 November 2008

Group 48 Battery

Last week was pretty cold. When I left work on Friday evening, I tried to start the car and it turned over once.... paused...... lights dim.... then turned over again and caught. I hoped the battery wasn't really dying, but I tried it Saturday morning after it sat overnight and the same thing happened, then again while I was out running errands. OK, time to replace the battery. This one had lasted 3 years and 50,000 miles, which is OK for an original battery. The one in my old GTI died completely after only 6 months. I replaced it with an Optima Red Top, which lasted the next 6 years.

Car batteries are referred to by their "group" number, which denotes the dimensions (length, width, height), terminal type, and terminal orientation (left/right). Here is a table that shows the measurements for different battery groups.

The battery that comes in the A3 from the factory is a Group 47 size. It has recessed terminal posts, and reversed terminals (viewing the long side when the terminals are closest to you, positive is on the right and negative is on the left). It has a heat-insulating blanket around it that must be re-used.

If you want a little better performance, you can install a Group 48 battery. The only difference between the Group 47 and Group 48 is the length, and the larger one will just barely fit in the A3's battery box. The original battery is only 480CA/280CCA capacity.

I wanted to put in an Optima battery, but they don't specifically make a Group 47/48 style. (I later learned that an Optima 75/35 can be made to fit.) Batteries are sold under several brand names which are all made by Johnson Controls. "Interstate", "Duralast" and "BOSCH" are three of those brands.

I chose a BOSCH Group 48 battery that cost $90.00.


It has a 850CA/690CCA capacity, 36-month free replacement & 96-month pro-rated replacement warranty, and came with a roadside assistance card for free jumpstarts for the first 36 months.


Remove the top cover from the battery box. Completely remove the battery hold-down bolt/plate with a 13mm tool.


Remove the battery cables, loosening the connectors with a 10mm tool. ALWAYS LOOSEN & REMOVE THE NEGATIVE SIDE FIRST! Also, INSTALL and TIGHTEN the NEGATIVE side LAST! I have 3rd-degree burn scars from doing it wrong years ago.

When you pull out the old battery, the insulating blanket will come with it. Slide the blanket off the battery. If you're installing a Group 47 battery, you can just slide it onto the new one. If you're installing a Group 48 battery, you'll need to look for the tab where the blanket is attached to itself, and undo it. It will wrap around a Group 48 battery, but with no overlap, so it's a little harder to get it back into the battery box if you're doing this by yourself. It does fit, though.

Re-attach the cables (see note above) and the hold-down, making sure it's actually holding the battery down securely.





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