Battery mAh and device operation
You can use either type. The only difference you might notice is how long the base station works when running only on batteries.  Compared to the 630mAh batteries when they were new the 600mAh will give slightly less operating time, the 700mAh slightly more. The base station should still work just the same and give the same signal strength whichever you choose.

The current drawn by the base station is not dependent on the capacity of the battery, just the time for which it can draw it.