Per there FAQ (Sounds like you need to go off the Wh rating which is much lower then the Ah rating they are advertising - not as good of a deal as I expected):
Q. How does the LFX "PBeq AHr" capacity rating compare to lead-acid Ahr ratings?
A. First, we need to understand that the primary job of a starter battery is to flow a large current (amperage) for a short time, in order to start a vehicle. In order to do that efficiently, the battery must have low internal resistance. Holding all other considerations equal, the larger the battery is in capacity the lower the resistance, and the better able it is to crank a vehicle under high loads.
Lead-acid makers have therefore used AHr(capacity) ratings as shorthand to indicate cranking ability, rather than a real usable capacity. The lead-acid capacity rating itself is based on a complete discharge at a low discharge rate. Under actual cranking conditions they will deliver considerably less than spec capacity. And because lead-acid batteries begin sulfating when only a small percentage of the capacity has been used, and their internal resistance rises as they are discharged, the actual capacity which can be USED may be as little as 20% of the mfg. rating. Discharge in excess will not only damage the lead-acid battery, it may not allow proper starting as voltage sags.
Shorai LFX are based on a completely different chemistry. Not only do they have less than 1/3 the internal resistance per capacity than do lead-acid, they are also the ultimate "deep-cycle" battery. The internal "completely discharged" capacity of a Shorai LFX is 1/3 the rated "PBeq" capacity. For example, the LFX18 12V series have 6Ah cells internally. But the cells are capable of 80% discharge without damage and while retaining more cranking ability. As such, the USABLE capacity(or "reserve capacity") of an LFX18 12V battery is on or very near par with 18AHr-rated lead acid batteries, while providing superior cranking performance and a vast reduction in weight. The Shorai PBeq AHr (lead-acid equivalent) rating system therefore allows users to compare a very different technology from lead-acid, but on a close apples-to-apples basis when making a choice.