I got mine on Amazon a year or so ago.....it qualified for free shipping....best price I found when that was taken into account. It is pricey....and just so you know, they moved their production from Colorado to Mexico a while back. it matters to some....

 

I went to Costco and got the Group 75/25 Optima Red Top battery for $128. Bolted right in with no issues. The cables had to be oriented into an odd position, but were able to still connect to the battery without modification. There is a small gap between the top of the battery and the bracket, but it's still mounted in place at the bottom, so it doesn't move.

So you might want to go that route if you have problems getting a 34R at a good price.

 

The 34 also fits....the difference between the 34 and the 34r is that the terminals are reversed. so you just turn the battery 180 and install...a few folks have done that according to the threads (The cable my need to be tweaked a bit...should be simple and self-explanatory like the 34R). I also want to get this clear...the Optoma is a premium battery, similar in cost to the OEM 200$ battery, but it is by no means the only option. Other company's make batteries that fit, do a fine job for less than $100....the caveat is it MUST have a VENTING system that is compatible with the cars (unless it is a sealed gel battery like the Optoma, which require no venting) or hazards can result...including explosions or excessive corrosion to the battery area. Group 34 battery's are actually bigger and more powerful than the stock requirement.....buy a bunch....resulting in longer life,more safety and more flexibility for the owners. The optoma batteries just happen to fit in the 34+34R size's.....other brands should be test fit!!

 

What happens when you disconnect the battery? Are there radio anti-theft codes? Air bag warning lights? Does this force a trip to the dealer?

I thought I was going to buy a $150 Optima 34R from Amazon, but then I read about what happens if there is shipping damage or the battery is defective.
They ship the battery by putting it in a box with paper packing. 3 out of 10 people reviewing the battery said theirs arrived broken/dead. Optima will not take it back because Amazon is not an authorized dealer. You can't send it back to Amazon because they say it is hazardous material. They ask you to take it to a recycle place and have a nice day. There is NO warranty. So I went to Autozone and bought one for $170. It is ready to go in as soon as I figure out the spacer issue. Thanks all.

 

Nothing should go wrong swapping out the battery. The clock and trip computer get reset, but that's about it. No need to go to the dealer. Just don't get the positive and negative terminals backwards and you'll be fine.

 

My battery from Amazon was fine...in a very welbuilt box, both hard foam. Was shipped ups, no problems. The battery was slightly weak, but nothing a good drive or 15 minutes on a charger would not fix. Since they are so much cheaper, and offer free shipping, it would not superise me if the bad reports were fom dealers who compete. Besides, when was the last time you took the time to complain when something from amazon worked right? So if they got 8 out of how many thousand dammaged, why worry.
If you are afraid to get one shipped, special order one at pep-boys, etc. It is a kick-azz battery.....great in the cold, and verry durable IMO.

 

Optima 35R from advance using the coupon code BIG40
will get you forty bucks off! I got my battery for $146.99 with tax witch is probably what you would get it on Amazon.com for..

This one has 920 CCA witch is near double the cranking Amps,But she starts write up!

The battery itself doesn't fit perfectly but it stays pretty nice I'm going to but a spacer on top to clamp it down better. And the terminals kinda stick up over the well edge a bit but it fits..

I'm digging it..

 

Well, 1 year minus 1 week, so I guess I didn't Jinx myself too bad . It's time to replace, and I've been doing some (re)searching (holidays coming, money's tight, but winter's cold, so...):

Found a chart of all recognized battery sizes (http://www.rtpnet.org/teaa/bcigroup.html) - using dimensions of stock 47 (246/175/190mm, L/W/H) and eliminating beyond certain sizes (too wide/narrow/tall/long/etc.). Considered width (front-to-back) most important, height close behind (effecting hold-down, required for racing events) narrowed down to:
26/26R, 34/34R, 70, 75, 78, 85, 86, 97R (all are 173-179 wide; I can fix 4mm w/ a dremel on the bracket, eh?).
Also 42, 90, 96R, but are shorter by ~15mm.
35 (mentioned previously in this thread) is listed as much taller, by 35mm (coincidence? ); maybe an Optima's shape may make it work.

Gonna try a 26(R) (208/173/197) or 70 (208/179/196); maybe the 38mm (1.4") shorter in length might save me a couple of pounds?

BTW: I don't need the stereo capacity, I barely ever turn on the stock radio...

If anyone has experience w/ any of these 'alternative sizes' (not already discussed above, please feel free to chime in!

 

Yup, that's the ticket!

Group 26R - Sears Auto, "Easy Start", 525 CCA (fyi: stock battery is 480), 60 month warranty (1 yr. full, rest pro-rated) > item # 22850227

Note: They carry 2 different 26R "Easy Start"; this one has "Manifold Venting" caps (but oval holes on both sides, do need to plug one side and do a little massaging with a drill bit to 'exhaust' tube on other, but nothing major).

Stock hold-down bracket and cables fit perfect, no spacers or massaging needed. Battery is a little narrower F/B (~1/4") and about an inch shorter L/R (as in 'less long'), and ~1/4 taller (once you pull off the handle - posts aren't recessed like the factory battery). Bonus: A few less pounds for the track.

Oh, and only $49.95 + tax (!) No ordering, in stock, bought and installed in parking lot in less than 10 minutes...

 

Then went out and looked at most of the options listed options and I purchased and installed a INTERSTATE MEGA-TRON PLUS (MTP-47/H5) battery in my 2006 Cooper S. The only tool needed was a 10mm wrench.

1. Same size as original-Fits perfectly.
2. Has the vent tube hole in the exact position needed.
3. specs on the battery are better than the original battery (880 CCA).
4. Cost $152 with tax and trade-in.
5. did not require modifying brackets.
6. 85 month warranty
7. The instrument warning lights are now back to normal.
8. It's just a little lighter

I have to complement the customer service people at Interstate battery who knew exactly what I needed and even found me a dealer that stocked the right battery 5 min from my house.

 

Great posts, I just spent about an hour on the web and phone comparing prices in the Seattle area. Here is what I found.

3 year free replacement:
Autozone Duralast Gold (H5-DLG) $135. On website, lists as 520 and 650 CCA, confusing. Probably a good option, anyway.
Interstate MTP (called Firestone) $140. I think this is probably the best higher end option.
Costco brand battery $65. Yes, still 3 year free replacement. 590 CCA. I'm going to buy this one.

2-year
Interstate MT, $95. 590 CCA.

 

Need to buy new battery , by what I have read it look like I will buy a Optima 34R is this the #8003-151 34R , why does Amazon say it does not fit my 07 MCS . $176.95 - $25.00 mail-in Rebate Offer from Optima . $151.95 free shipping .

 

Just wanted to thank everyone for the info. I bought a 2006 MCS new and the battery just died for the first time. After reading everyone's reviews, I got the Bosch Premium Performance Battery Group Size 47 from Pep Boys (http://www.pepboys.com/product/details/9073731/00288).

It fits perfectly. And they have an online coupon (secret35) that saved me 35%, which was a huge help. Thanks again!