Instruction: Generate an answer to the question by utilizing the information contained in the document.

Input:
Question: how long it takes to charge the unit
Document: I charge a variety of items with this unit so how long it lasts depends on what you are charging. Everything takes a different amount of time, so the longer you need to charge the fewer times you can use it before you need to charge the unit itself.For the convenience of being able to charge on the go I love this item and would definitely purchase again.
Works great. Takes a while to charge the unit up but it lasts a long time too so as long as you remember to plug it in the night before it will give you more than enough power to charge your phone a few times. I did have to use the 2A outlet on the unit to charge my phone, it would not charge on the other. I charged my phone twice from just about dead and charged an old ipad on one charge.
No more worries about running out of power during  long day trip hikes so unlimited picture opportunities ahead. So far so good,  will respond back later on once I have used it more often. The one thing to be aware of is that the unit itself takes along time to charge up, this should be expexted since it holds such a large potential for power. This is in no way a setback but a warning to those who expect it to charge up like your phone.
I've had it for a week now and it is living up to its specifications. I use it to charge my iPad 3, iPhone 4, and Kindle. When charging the unit itself, it takes about 8 hours to go from 25% charge to 100% which is what I would expect for the specified 1500 mAh/h Input Charging rate.
This unit is as written big and bad. maybe because i try to charge a mobile phone ( galaxy s2 that it takes a week to charge.the phone actually starts to get hot. so maybe i can use it to heat food up.time to look for something else. when i called anker they could not supply a time that it should take to charge a phone. ooofffaa !
I use my phone at work to stream music to a bluetooth speaker so it is running pretty much all day but a quick charge from this unit is all it takes to keep my phone going all day. I do not always have the opportunity to plug my phone in or swap batteries. I really like it for charging up my Ipod too. For something hardly bigger than a deck of cards it really stands up to heavy use.
This is probably the best thing about it, as you can actually charge the unit overnight. I've found that the RavPower unit, on the same outlet, often takes in excess of 12 hours to fully charge (and it has less capacity). Furthermore, the Astro E5 charges gadgets faster than the RavPower despite what is supposedly the same amperage out. I attribute this to it simply being newer with better technology and components. To be fair, the RavPower is an older generation unit that is also cheaper and smaller.
It's easy to see how much charge is left via the indicator lights. The flashlight seems fine, although I don't think it's particularly useful - I'd have just as soon saved some weight. However I have no problem with it coming on accidentally as some reviewers had complained of. Having the 2 charging ports gives options for multiple devices. It takes several hours to fully charge, but that's to be expected as it's a powerful unit. Charge time for my iPhone is very comparable to charging it off its own adapter.
works very well, lasts a long time, takes a long time to completely charge.
OK and working. Takes  pretty long time to charge but not getting as many recharges as claimed. Otherwise no complaints.
Answer: From zero, takes about 12 hours.  When you have about 25% left (which is what I have after a weekend of traveling), 6-8 hours.  That is with it hooked up to my PC via USB.  Not sure if you plugged it into the wall.