98 E430 has starting problems

Hi,
My E430 would not start today morning. The whole of last week, because of the holidays andschool being closed, I drove the car for very short trips of
less than 0.5 mile. I got a jump-start which started the car so the battery did not have enough juice to start the car. After I drove it around for some 20 minutes, the car started again.
The car is a 98 E430 and has been running on the original battery for some 7 years, I presume the battery must be reaching end of life. Because of the holiday weekend all repair shops are closed and it looks like I will need to change the battery myself.
I need some recommendations on a quality battery, the local MBZ parts dealer told me that the replacement battery from MBZ is not the same part# as the original, MBZ now just has 4 different batteries or part# for all their cars. Also its costs $125 for battery and $75 to install it.
I plan to get the battery load tested at AutoZone or Kraegen after the holidays, in the meanwhile I would like advice from the group on what other possibilities the car starting problem could be related to. I would like to mention the weather could also be a contributing factor since it has been wet and cold throughout the week.
Also advice is solicited, on a replacement battery and tips to install the battery so that the car settings/codes are not lost.
Thanks in advance,
John
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Just buy the battery at Autozone... they got the best deal on battery with 7 years warranty.
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I also like the NAPA batteries. I got one for my '95 several years ago.
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