In-situ charging LT1505


I want to be able to charge the batteries while the system is running. The only charging circuit I've found that isn't to tiny for soldering is the LT1505 and as such it's purchased, however something has struck me. Where it says to system power, will that be at the level of the adapter when connected?

lt1505 datasheet:

One of the components I will be using needs 12V (a psu) - if it is as I suspect the voltage will range from 10V to 18.5V, any way to make that be 12V?