Before we get into that, we'll take a look around the Genius ECO-u821 charger.
Once the ECO-u821 is out of the box, the fun begins. Looking at it top-down, the only thing we can notice is the Genius branding.
On the bottom of it, we have the details of what we can find inside of it - the battery size, voltages, and of the labeling to what the ports are on the side of it.
To the right side of the Genius ECO-i821, we find a charging cable tucked away. This is a thin charging cable that tucks right into the side of the ECO-u821, which is great.
At the rear of the charger, we have the two USB ports - one 1A port, one 2.1A port - and the micro USB port for input. Now that we're done with the pleasantries, let's get into it. Genius' ECO-u821 is beautiful. I love it, it's sleek, it looks great, and it's thin and light. After testing countless mobile rechargeable batteries, this is one of the best that has come through my lab.
Genius has a thin, light charger (like GOAL ZERO SHERPA 100 KIT ) that packs plenty of juice inside. If you were to lift it and feel the weight of it, you would guess that there's a ~3000mAh battery inside. Somehow, most likely with magic, Genius has slammed 8000mAh into it, all while looking great, too. It is quite a large charger, but the low weight offsets this big time. I used the Genius ECO-u821 on a trip away with my wife and daughter for a few days, where I exclusively used the ECO-u821 charger to keep my Nexus 5 smartphone topped up. I was able to go the entire trip - three days - using just the Genius ECO-u821 charger. For me, this is great, as it means I can sit in my hotel room, anywhere in the hotel room, with a fully charged smartphone. Better yet, when I was packing my bag, the thin profile on the ECO-u821 came into play once again.
I was able to slide it into my bag against my tablet, which is obviously also flat, and they sat together well. Most rechargeable batteries are thick devices, and they have no place next to another device. Genius' decision to go thin, and light, makes this one of the most standout batteries I've tested. Considering you can grab them for well under $45, it has to be one of the best-priced mobile batteries around. I have no hesitations recommending this to anyone who is in the market for a new mobile battery; with 8000mAh of charge, it will charge even the most battery-hungry smartphones a few times over, all while looking sleek.