The battery isn't that bad, it can last a good 20 hours on one charge, depending on settings (example - turn brightness down). Also, I have charged from close to 0% and it usually takes an hour to get to 100% for me. Make sure you use the cord it came with for best results.
I have used this phone in a pool, but as said before, it's not waterproof, but is water resistant, as long as the USB and back cover are all the way closed. As for the USB cover, it has fallen off for many users of the normal s5 and probably people with the Active also. Mine hasn't yet, but it isn't as secure as it used to be. I think it's because some people have a hard time opening it, myself included.
Make sure to find a good case, something that has an edge that sits above the screen a bit, because the buttons and screen are very sensitive to touch, and the phone can activate easily. If you decide to do pattern lock to help with the occasional random opening of apps or pocket dialing someone, watch out for the on screen 911 touch button. AT&T never put out the newest Kit Kat update (they're waiting for Lollipop instead), which fixed pocket dialing 911.
It's a great phone, has a lot of life, just a few quirks here and there.
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