Just have to share this since I have been super happy with mine, and replaced my older portable battery too. Also, I think having one of these will be an absolute must if you are going to have your switch with you on the go a lot like I will.
If you have followed rapid charging for newer Android flagship devices, you will know how much of a dream device this is and the last I checked, the only one in existence that offers what it does.
First, the ravpower (link below) has qualcomm quick charge for INPUT. This battery will replenish much faster than any others on the market simply because of this. However, it requires one of the qualcomm quick chargers for this feature or you will be using normal "speed". (and iirc, not included, however you can find qualcomm QC both car and wall chargers on amazon for fairly cheap now).
Second reason for why this is amazing, is the USB-C port (and my reason for posting here in this sub). Since the Switch will have a USB-C port for recharge, this ravpower model also outputs the highest amount of amps that is 3.0A. USB-A to USB-C can only output a max of 2.4A and does not qualify for Android phones rapid charging feature. A bit of history: the Nexus 6 supported qualcomm's version of quick charge. Google decided they didn't want one company to be able to corner a market and become a standard. They chose USB-C (other reasons also) for the Nexus 6P and beyond and chose 3.0A universal charging rather than having to rely on a specific brand's chipset.
Third, this bad boy is 20100mAh! Their site claims "Charge an iPhone 6S 8 times" but things like that are a little more perfect world and your results may vary some. I get a bunch of charges on my Nexus 6P and usually recharge before its completely drained.
I have my fingers crossed for the Switch supporting rapid charge like android flagship devices do!!
If you have any questions on amps, limitations, and other things I can probably answer them. I follow the types of chargers and what is needed very closely since I have upgraded to each of the new nexus phones every year and have replaced every charger I own multiple times.
I should also disclose that you will need to purchase the qualcomm QC charger separate like i mentioned above, and the USB-C to USB-C cable isnt included either and you will need to acquire one of those as well.
Discussion started at here by s1ncere