I use an
O'Reily's Group 48 Super Start Platinum AGM battery in my 2012 Golf R. 70 AH, 120 RC, 760 CCA.
Its length and width are pretty much exactly the same as the oe Varta.
No issues with the insulation sleeve, fits the same as oe.
The O'Reily's Group 48 battery is slightly different in height, but not enough to make any difference at all.
Battery box, insulation sleeve, and battery cover all fit without issue.
I seem to be hard on batteries.
The oe Varta battery died in about 2 years at 60k miles.
I expect an AGM battery to last longer than an oe battery.
I installed the O'Reilly battery in the Fall of 2014 and it seemed fine.
However, in Fall of 2016 (just short of 2 years, ≈50k miles),
it starting giving me trouble, forcing me to jump start.
Took it with my original receipt to the same store I bought it from to be tested.
They did not bother to test it, they just swapped it out for a new one, no questions asked.
So while it gave me some hassle what seems to be too soon,
it did not cost me anything to have it replaced.
Ultimately, even if the replacement fails just as fast,
I will end up with 4 years of use for the original $$ outlay.
4 years is what I typically expect from a battery.
anything after that is bonus too me.
As for the comments about getting by with lower rated batteries,
as long as you are in ideal conditions, should not be much of an issue.
Just keep in mind, if you deal with extreme cold, it may be an issue.
The reserve capacity rating is the time (in minutes) that a lead-acid battery at 80 °F (27 °C)
will continuously deliver 25 amperes before its voltage drops below 10.5 volts.
Assuming that rating is 120 minutes,
at 32 degrees F, typical capacity is reducted by 35 percent (78 min);
at zero degrees F, it is reduced by 60 percent (48 min);
and at minus 20 degrees F, it is reduced by better than 80 percent (24 min).
I occasionally have to park outside overnight
(at hotels) in Michigan and Canada in January / February.
For me, that is the least convenient time for a battery to come up short.
i.e. I am unwilling to risk any significant under-rating
so as to avoid the worse case scenario.
And with the first and the current O'Reily's Group 48 batteries,
have had no issues in those cold conditions.