is battery charge rating of iPhone DC5V?

Yes, that's what it requires. The real number you should be looking at is the wattage. 5 watts is low, it will charge but take a long time to do so. 10 watts is better but will still take longer to charge. Anything over 20 will be good, it will charge faster with a higher wattage rating. You can't overcharge so don't worry if it's a higher number.

Not sure what you asking.

DC5V means it's 5 volts Direct Current. That's is what a USB voltage rating is.