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Discussion Starter #1
Normally a battery "ages" as the active plate material sheds (or flakes off) due to the expansion and contraction that occurs during the discharge and recharge cycles.

Deep discharges, heat and vibration accelerate this "aging" process. Eventually, the sediment builds up and this can short the cell out.

Another major cause of faulty batteries is sulfation. When batteries are stored discharged or for over six months, lead sulfate makes the plates very hard and dense and the battery less capable or unable to be recharged. When the active material in the plates can no longer sustain a discharge current, then the battery "dies".

In a hot climate (the harshest environment for a battery), a recent survey of junk batteries revealed that the AVERAGE life of a good quality car battery was 37 months.

Slow cranking, especially on a cold day, is another good indication that your battery is going bad and it should be tested.

I'm writing this because today, I had to jump-start my 325i. I looked around these post and found mostly incomplete information. I knew I didn't want a Dealer battery, so I went searching. My research was on the E46 and I heard there is a different battery for the Convertible, so this may be incomplete.

The Battery Council International (BCI) sets the standard on batteries. They are divided up into group sizes by Dimension and OEM Cold Cranking Amps.

My local parts store (Advance) showed me 2 batteries that would fit my car and of course they wanted to sell me the most expensive one. Here is why I didn't listen to them.

Unless you are racing and are worried about weight or want a gel battery, the rule of thumb is like "D!ck Measuring". Bigger is better. Voltage on most of our cars is always going to be 12 Volts. More Amps is what we are looking for.

Buy the freshest and largest Reserve Capacity (RC), battery that will physically fit, with a Cold Cranking Amp (CCA) rating for your climate that meets or exceeds the car's Original Equipment Manufacturer's (OEM) cranking amp requirement.

Group size 94R is listed for most E46's.
Group size 49 is listed for some M3's.
Group size 92 is listed for some M3's and Convertible's.



I am unsure if the 92 battery is for an E46, the years matched in the parts book. The 92 battery is shorter.

The 49 battery is physically much bigger (length) and has a higher Cold Cranking Amps than the 94R. And guess what; it was also less expensive.

My advice for most E46's:
"Battery Warranties are just marketing"
"If it fits in the battery box use the Group size 49 Battery."

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PSHOPWERKS
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AutoZone 49-DL.
 

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Discussion Starter #4
My point is you don't have to use "AutoZone". The "-DL" is just their numbering system. It probably means "Delux" or some [email protected] thing to do with warranty or marketing.

If you don't have an "AutoZone" close, just ask your local parts store for a "group size 49" battery. They should know what you mean. If the person doesn't know, ask to speak with someone that has a brain. This is a very popular battery.

I bought mine from "Advance". "AutoZone" was across the street from this store. Same price, same size, same color. "NAPA", "CarQuest" also had them in stock when I called them.

P.S.
I am going to post a DIY on this very battery install.
 

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48 was also ok to replace my 94R

NAPA 7548 (group 48), fits fine. 12.1" x 6.9" x 7.6" top rated by Consumer Reports. $76.49 at NAPA. Dealer $180.
 
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