2600 mah vs 5600mah vs 12000mah vs 20000mah?

I want to know how long each one last. I will be using it to charge my iphone or computer. They are for back up battery.

There's an easy way to do this and a hard way. 8^) The easy way is not exact but it should give you an idea.

Look at the battery in your phone. It is marked with an mah rating. My Girlfriend's is here and I just took the cover off and the rating is 750 mah. (That's just a regular flip-phone. I think a newer smartphone would be more than that. But it's marked on the battery inside the phone).

So how long does your phone last you on one charge? I charge mine every day but it might last two days if I don't use it that much. That's 750 mah worth.

(BTW if you didn't know, mah is milli-amp hour, meaning the battery will put out 1 milliamp for 750 hours.)

So now take 2600 mah. Divide that by 750 and you get 3.467. That means that 2600 mah battery will recharge your phone 3.467 times (more times if the battery isn't fully discharged), or keep it going 3.467 times as long if you just keep it plugged in.

Now that's not exactly right because you don't get 100% efficiency. You lose some of the power in the transfer. Maybe 15% (I'm guessing. It might be more. I doubt it's much less). But that's roughly the number.

I have a 50000 mah battery that I use to keep my cellphone charged on my motorcycle, because I use it continuously for the GPS. I just keep it plugged in all the time I'm on the bike. It's really amazing, it keeps it going for days and days!

So, bottom line, look at the power in your battery, divide that into the power of the charging battery, and that's how many times the length of one charge you will get.

Obiousy it is the 20000 one. The larger the mah count, the more amount of harge it can hold. But larger the capacity, the external battery tends to get bulkier and heavier. So if you only want to charge your phone and not your computer, get the 2600 or 5600. But if you want to charge your laptop as well, get the 12000 or 20000 one as the others will probably not even charge it 3/4.