Jeff,
On my 2007 Prius, the Info + cycle-headlights method fails to enter maintenance mode. The display does reboot, but it returns to the normal display rather than to the maintenance menu. On the other hand, the Display + touch-sequence method does work, using the sequence UL-UR-UL-UR-UL-UR. Thanks.
So Toyota makes changes from year to year. This shouldn't surprise us.
(BTW, this reveals my battery voltage to be only 9.6 V, presumably explaining recent failures to start. Is three years a normal time to failure for the auxiliary battery?)
Our Prii use a "Constant Voltage" charging protocol. This is a simple way to ensure that the 12v battery is never overcharged, but also means that the charging is very slooooow. If you regularly drive your Prius for long drives, this system does a reasonable job of maintaining the 12v battery at full charge (My 2004 at 168k miles is still on it's original 12v battery). If you drive a short commute, the battery will tend to discharge and lead-acid batteries require storage at full charge or they will fail prematurely.
One way to maintain any 12v battery in good health (if you have access to a 120v outlet) is to use a Battery Minder in your garage. The one to get is:
http://www.batteryminders.com/batter...--p-16151.html
It is about $60.
JeffD
ps. A Battery Minder may revitalize your existing battery if it is not too far gone.