Does having 2 identical lithium battery packs double the ah capacity?

#1
I am about to buy a lithium battery pack for my ebike. It has an 800w direct drive hub with matching 36v controller. 2 x 36v 15ah battery packs are a lot cheaper than one 30ah pack. If I wire them in parallel will they theoretically give the same performance as the single 30ah one? Apart from doubling the size and bigger weight, is this a feasible and practical idea?
 
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