BikeBatts.com

Battery performance and capacity is typically rated in terms of  Capacity (AH) and cranking performance in terms of Cold Cranking Amp (CCA).

1. Capacity is determined by a slow discharge (usually over ten hours) until the battery reaches 10.5 volts. The test current multiplied by the discharge time is the capacity in Amp-hours (AH). This is proportional to the volume of the plates and acid, i.e., the battery's physical size. The relatively long test time allows diffusion to replenish the weakened electrolyte in and near the plates, ensuring that most of the sulphates in the acid can be used.
2. Cranking performance is usually measured in Cold Cranking Amps. CCA is the highest current the battery can supply at 0° F for 30 seconds without dropping below 7.2 volts. Due to the short time and the low electrolyte temperature, diffusion is negligible and only the acid in the plate surface can be replenished at all. The weakened acid inside the plates cannot be replenished in such a short time, so battery CCA is directly proportional to the total plate surface area, the negative in particular. The eventual replenishment of the weakened acid is what allows the battery to "recover" when you pause after prolonged cranking. Keep in mind, actual cranking power increases with temperature; the CCA number only applies to 0° F. Sometimes you may see a reference to "CA", or Cranking Amps. This is the same test, performed at 32° F.
3. Battery selection, then, depends on how much cranking power and capacity you want. Larger batteries generally have larger plates, providing both increased volume (capacity) and surface area (cranking power).
   1. You need a good CCA "safety factor" for very cold weather and hard starts. Hard starts can include poor state of tune (long cranking required), thick oil, high compression, and so on. A new sportbike will typically require very little CCA to start, even in winter (the stock battery had less than 180).
   2. You need good AH capacity if you are running accessories, winches, extra lights, hand or suit warmers or load-leveling concerns. A higher capacity alternator will, in most cases, address electrical load demands placed on your battery and system. A higher capacity charging system may also allow you to use a smaller battery and save weight at the same time. Use a larger battery if you want to error on the safe side.
4. Battery life is another concern. The cycling action weakens the positive plate over time, causing it to slowly shed particles of the active material. Larger batteries will be used to a lower "depth of discharge", causing less of the weakening. Furthermore, the loss of that material will be less significant since there was more to start with. In practice, these effects are probably small, unless you run with a lot of "load leveling".

Cold Cranking Amp capacity for BikeBatts.com  Xtreme Volts and Ultra batteries are rated at @ 0 Degrees. F, -18 Degrees C for 30 Seconds with 1.2 volts per cell minimum