Hi all,
Based on some calculations I did, using a 35mA draw (15mA immobilisor, 20mA alarm), it appears that an Odyssey PC680 (what I myself have now - it came with the car) will reach 50% capacity in only 6 days, under ideal conditions (80F). Anything colder, and 50% would be reached quicker.
The PC680, according to Odyssey, is not designed for reserve capacity. Assuming that starting the car requires at least 150A, a PC680 rated at 300CCA would not last more than 7 days before it struggles to start the engine.
The PC925 should reach the 150CCA point after around 17 days.
The PC1200 should reach the 150CCA point after around 30 days.
These calculations assume a relatively linear power drop, and in an AGM-based battery should be relatively accurate. Wet cell would probably be more unpredictable. The calculations seem to fit the relative experiences with the different ratings I have had.
Note that CCA is taken at zero degrees celcius (32F), so under "normal" weather conditions, you should be able to gain a little more time. However, since the reserve power ratings are done at 80F, it may compensate for this gain.
DISCLAIMER:
These calculations are an approximation, and the age of the battery, condition of the charging systems, use and abuse of the battery, etc, can (and will) have a major impact on the figures.
If weight is a major concern for you at the track, but you drive on the street too, then I'd suggest getting a PC680 for the track and a PC925 or PC1200 for the street. Just swap the battery when you get there.
AGM-type batteries can be stored up to two years (make sure it's fully charged before storing). This will ensure the best battery life overall - IMHO, PC680's on the street cycle too much, reducing their lives significantly as the battery should always be kept nearly fully-charged (unless you have a power outlet nearby with a
good battery maintainer!).
One other thing - you should also ensure your regular charger is designed for AGM-type batteries.
HTH!
Thanks!
S.