I dont think you need a belt. I tuck mine in my pocket, or man bag.
There are lots of crap battery charges on the market (ive tried them
) but if you want a good one with tons of good feedback and my realworld usage the ankers are the best.
https://www.amazon.com/Anker-PowerCore-20000mAh-Portable-Qualcomm/dp/B00VLNT9KW/ref=sr_1_1That is the one I have and I can charge mine and my wifes phone at the same time, both getting a full 2 amps in about 45 minutes. And it has enough juice to do that at least many times. Ive charged just my phone fully 6 times before it was depleted.
Most people shop just based on the mAh of the pack, but most of those are misrepresented on the knock off brands. The capacity and amp output are the key figures though. 2A with cabling (28/24AWG) to properly carry that 2A means you can fast charge alot of devices.
These are the cables I use. I like 10ft, but they come in 2,4,6 as well.
https://www.amazon.com/Monoprice-10-Feet-Ferrite-Plated-108642/dp/B009GUQ1N0/ref=sr_1_1When people ask me if I have a charger and they use mine, the comments are always.. wow how is this charging so fast, and also... where did you get the 10ft cable.
Note that anker also makes cables that carry 2A but they cost more and I found they didnt last as long, so I buy the ones I linked.