It depends on how much current your phone processor is taking to run different apps. Capacity or charge in a battery = current * time. so your battery runs for 10 hours. If you are running only fewer apps on your phone, then the current will be less than 300 mA and the battery can run for more than 10h.
Likewise, what does mAh mean for portable chargers?
A rechargeable battery's capacity is usually measured in milliamperes (mAh). For example, a Samsung Galaxy S3 comes with a 2,100mAh battery, while the iPhone 5 relies on a 1,440mAh cell. It stands to reason, then, that any portable charger you buy should have at least as much capacity as your smartphone.
Is it better to have more or less mAh?
Batteries with larger mAh ratings generally last longer than those with smaller ratings, assuming that the batteries are subjected to the same patterns of usage, but it may not mean a better battery. The milliampere hour represents a unit of electrical charge commonly used to measure battery capacity.
What is a good mAh for rechargeable batteries?
The mAh capacity rating refers to the storage capacity available for a particular battery. A battery with a capacity rating of 1800 mAh could deliver a current of 1800mA for one hour. Higher mAh ratings for the same battery type will generally mean longer run times.