I'm shopping for a portable charger to use while we're in the parks (so I can check the TP and MDE apps without worrying about my battery). Any suggestions on what I need to consider before buying one? Also, I'm noticing they use lithium batteries. Are these okay to carry-on planes?
You can carry lithium batteries on airlines IF they are in your carry on or personal bag. They cannot be in checked baggage. Check the web site of your airline for details.
That said, I have this one: Aukey PB-N15 20000mAh 3.1A Dual-USB Portable External Battery Charger which is $25 on Amazon. It will charge the average smart phone or tablet from 0 to 100 several times, (My Samsung S6 battery has a capacity of 2,550mAh, and it will charge it 6 or 7 times, for comparison), and does so fairly quickly. It also has two output jacks, so will charge two devices at once. However, it is HEAVY. It's right at about one pound, which gets to be pretty weighty in a bag you carry around all day, along with everything else. There are others with lesser capacity that weigh in around 6 - 8 ounces. I'm thinking about this one for our next trip: Anker PowerCore 10000 Portable Charger.
I have a Mophie and love it. I can go from 25% to 100% at least twice (never needed more than that) on my iPhone 6 with no problems. It;s also quite fast.
If your a AAA member and you sign up for their Visa you can get one for free. It is the size of a lipstick tube.
As mentioned Anker is a top choice. Ravpower is another very good option. I would recommend something around 10,000mAh capacity.
Why not use the FuelRods available at WDW? If you buy one of those, you can trade it any time it runs out of charge (there are kiosks at all the parks and I believe all the resorts now too) without having to pay to trade it in and then you won't have to worry about charging it every night.
EDIT I just realized this post was brought back from the dead.