Recommended power bank capacity for iPhone 4S I would like to know the recommended capacity in a power bank to charge my iPhone 4S on the go. 

I've seen power banks with over 4000 mAh of capacity. Wouldn't that damage my iPhone, since I read that the iPhone 4S has a battery of 1430 mAh and the charger is 1000 mAh.

Wouldn't the recommended capacity be around those values?

And one more question, how do we calculate how the iPhone would charge? For example:

I have a friend that has 2 power banks, one of 4400 mAh and other of 2600 mAh. She says that she can charge her iPhone twice to 100% with the 4400 mAh power bank and she can only charge to 80% with the 2600 mAh.
The power bank capacity is just that, capacity. So the bigger the capacity, the more often you can recharge your iPhone before you need to recharge your power bank. Give or take a few mAh getting lost on the way, the number of recharges possible is basically Capacity of power bank divided by Capacity of iPhone.

This also means that there is no recommended capacity per se. Questions you may want to ask yourself before buying one include


do I need to recharge several time a day or is one recharge usually enough?
do I plan to take multi-day cross-country hikes without power outlets on the way
is low weight important for me (more capacity usually means more weight)
do I just want to recharge one device or is the goal to charge e.g. an iPad as well