In addition to the good advice you've received about the real amperage of the pack, I'd check via email that it is gauranteed to be 12s. I've seen a few dodgy adverts for 36v lifepo4 in recent weeks wherein, if you look at the fine print or ask the seller specifically, they are actually selling 10s (usually 10s2p made with 5Ah cells). Even some of the more established sellers like cohinsmotor are doing it, but at least they're upfront on their website (Yet, how many of their purchasers actually know the difference between 10s and 12s and can therefore understand that what they're getting is NOT cheap?) The hot off the charger voltage may be close to 36 (and, even then, they've probably set the BMS and/or charger to allow overcharging which will decrease the life expectancy of the pack) but, when combined with the fact that these are made with 1C pouches, the surface voltage will disappear in no time. The suitable for a 250w claim makes me even more suspicious that what they've got is actually a 10s3p 30v (i.e. THIRTY volt) battery. A 5A charger for 1C cells? (also dodgy - even the 2A charger might over do it)
However, having stated all that... if you live in the land of the dingos, as is indicated by your username, a 30v might be a nice way of keeping close to 250W if you want to be almost legal. Just be careful that your controller and/or bms doesn't have low voltage cut-off at 31v, as many of the 36v controllers do.
To my mind, pre-made headway packs are the best bet for 36v shipped to Australasia. I got a 12Ah 12s1p sent out from china for US$350 incl shipping recently. That included capacity based balancing and headways which are stated as 5C but, even if they're only 3C, that's good for my present needs, and for expansion if I go to a higher rated (and probably illegal here in NZ) motor.
