bq27541-G1 to be used with 4S battery packs

Yes, you can use the bq27541-G1 in a multi-cell application. However, the '541 is a single-cell gauge and TI does have battery gas gauges that are meant for use in multi-cell packs, such as TI's newest gauge, the bq40z50. Is there a particular reason for using the '541 in your application?

One possible method is to power the '541 from the top-most cell (to avoid creating an imbalance between the bottom cell versus the rest of the pack), and measure the voltage of the bottom cell (see TI app notes SLUA387 and SLUA300 for hints; they're for different single-cell gauges but the idea is similar). The maximum input voltage on REGIN is 24 volts, so although the 16.8V input of a 4S pack won't damage the gauge, I'm not sure what effect it would have on the gauge's power consumption. A voltage divider to scale the pack's voltage for the BAT pin could work, but keep in mind about that divider's power consumption.

Jason's options are good, and we also have customers who use the voltage divider scheme from SLUA496 with bq27541.  You can connect REGIN to the top of your stack, and the divided voltage to the BAT pin, as Jason mentioned.

http://www.ti.com/lit/pdf/slua496

If you plan to have a gauge inside the 4S pack, usually you might want to choose a multi-cell gauge that can do cell balancing and other battery management functions (like safety).  However, to save money you can use a single-cell gauge like bq27541-G1 with this method, as well.