HOW TO batch Geocode a set of addresses
Geocoding is the process of taking an address and getting the associated latitude and longitude so that it can be visually represented as a a point on the earth with any mapping service.
MapQuest API has a free batch geocoding service that allows multiple locations to be geocoded at the same time. A limit of 100 locations exists for one call. I haven't seen any of the popular mapping services offering this kind of a bulk geocoding facility.
An AppKey is needed to run that service & you can get it by creating a free Community Account.
An AppKey is generated when requested but it will take approximately 1 hour for your AppKey to be active.