I'll have to disagree with tllim here. That battery is rated for 500mA max, which at best means somewhat<500mA continuous and at worst substantially less - misstating lipo battery specs is common even for branded cells, let alone generic no-name ones off of ebay. The likelihood that Pine64 will only ever consume < 500mA is 0. As such, you'll be using a substantially under-spec battery. Keep in mind that lipo is *not* a safe chemistry - exceeding the discharge rating is asking for a fire.
The correct way to establish what battery you need is to take the board + all the peripherals you intend to attach, run it at max load and record peak current plus, say, 95th percentile high and use that to qualify the battery system. No one can tell you what your high is, since we don't know what power-drawing peripherals you're going to attach. Alternatively, use a safe chemistry battery instead of lipo to begin with so the penalty for exceeding the power envelope is a brownout or reboot, rather than a raging inferno and the disconsolate wailing of innocent children, spouses and pets.
-p
The above is in reference to the ebay battery. Although I have no knowledge of the 8000mAh battery pine64 is having designed, it's much more likely to be workable - assuming peak 2A that's just 0.25C (google C rating if you're curious) which is eminently within reach even for el-cheapo lipos. It's unlikely to be cheap, certainly nowhere near as cheap as an a priori unsuitable, under-spec mystery cell off of fleabay, but you need to factor in the cost of a new house/family into the equation
If you're going to run marginal lipos, at least get a fireproof charging bag (rc stores sell them usually) to run the whole thing in for some measure of safety.
-p