I recently got the 5,000mah powerbank (https://www.ozbargain.com.au/node/197734). I think it was Xiaomi brand for about $10US. It has worked well for the couple of days I've had it.
Then I found this one:
http://www.newfrog.com/p/ultrathin-20000mah-external-battery…
It's supposed to be 20,000mah for about $13-14US. Is this a good deal?
Ok thanks. Will leave this one be.
High capacity Xiaomi powerbanks are pretty kickarse, and they usually hover around $20 bucks delivered. Use cashrewards for even bigger discount.
I've gone down the route of DIY powerbanks as well — you buy the 18650 batteries (unprotected, flat top types) and the USB enclosure seperately, then create your own powerbank, but it is not as cost effective as buying a Xiaomi. Just stick with what you know works best, especially when it comes to batteries.
I have never used it before however a general rule is that if its too good to be true, it probably is.
It may not actually be 20000mah and the batteries are probably some generic brands. I personally would just go with a reputable brand as they are more reliable and safe.