I've been looking around and considering getting one of these gadgets and there are so many around. I got one from Amazon, very cheap and nice design, but will be returned as it's only 3000MaH, gives me about just over 1 hour, and I see now I need at least 8200.
So has anyone found one they really like, that's not too bulky, not too pricey and can add at least 3-4 hours of use time.
FWIW, I recently purchased a compact "boostbox" for my truck.
It's an AllStart 550 with 12,000 mAh capacity and is able to charge from 5V USB or 12V vehicle powerport/lighter.
Since then all my spare batteries and my jumper cables have to find a new home.
At 3"x 6"x 1.2" it is the same size as 3 Galaxy S5 cell phones stacked together.
They claim 1,000 charge cycles.
It incorporates a multi mode LED flashlight and jumper cable pigtail plug.
While this is way more that your $30 battery, it charges fast on 12V and fills more than one need for me.
Using the stock Samsung USB to micro USB cable that came with my Note, the kids have watched videos for 3 or more hours in the back seat.
I have no idea how long it will really run the tablet.