I charge all my gadgets using the Tank's solar powered house battery bank. Most of the time there's more than enough electricity to charge my cell phone, mifi modem, Kindle, etc. Occasionally I run into a streak of poor solar days like rain or dark clouds and I wished I had additional power stored. To address that issue I purchased a 10,000 mAh (milli-Amp hour) storage battery.
The battery comes with usb cable and carrying bag.
The battery is from Amazon's Amazon-basics offerings and cost $29.95. It's slightly larger than by Samsung S4 cell phone and weighs 7.25 ounces. I like that it is very simply designed. There are two USB ports on the side, one a 2.4 amp and the other a 1.0 amp. You can use both ports at the same time for charging purposes.
The side charging ports with the middle one for charging the battery itself.
As soon as you plug into one of the ports the battery automatically comes on and starts charging. You determine how much of a charge the battery itself has by looking at four blue LED lights on the front -- 4 lit means it has between 76 to 100%, 3 means between 51 to 75%, etc.
The charge LED's, the 2 marks denote the 2.4 amp port, 1 denotes the 1 amp.
You can charge the Lithium-ion battery by using a USB port on your computer/laptop and since Amazon doesn't ship an AC charger with the battery you might have to. A faster charging method is to use one of the many mini USB AC adapters from your OTHER electronics that are lying around if you're like me. The one to my Kindle works fine and its WAY faster than using a USB port to charge the battery so I really recommend it.
So what does 10,000 mAh's give you? Well, my Samsung S4 has a 2600 mAh battery so I could almost get 4 complete recharges from the Amazon-basics battery. My Kindle has a 4600 mAh battery so I could get two full recharges to it. Obviously, we seldom completely drain our devices so you can see that the battery could charge a number of your USB-chargeable devices on a single charge of it's own. I haven't owned it long but so far it's gone a week and seemingly retained a complete charge.
For as little as it costs, and as transportable as it is, the battery is an excellent back up for heavy cell phone users that struggle to get through a long day on one charge.