Donīt remember about the APU BATT, but during my 737 days (3-400) BUFFET ALERT was when you were on the border of the stall protection (1.3G in our case, probably some operators 1.5). When you really get into a buffet situation in a B737 Classic, you wonīt miss it.
ANS NAV or Alternate Nav is IRS only, not many operators with this option, but as we flew oceanic in MNPS we needed it to fly without restrictions. Really much like using the old INS.