The bus volts indication on my G1000 is pegged at 29.2 volts for both the left and right bus. I have a 24 volt system. What might that mean?
the output voltage of a 24 volt system will be slightly less than 24V. the charge voltage will be significantly higher than 24 volts in order to push the charge into the battery. It therefore sounds like the battery charging circuit is stuck "on" where what it should be doing instead is continuously cycling on and off, on and off as the engine runs at cruise to keep the battery "topped off".
The charge system is regulated by either a mechanical relay or an electronic switch that senses system voltage and engages the charge function whenever the system voltage drops below a fixed threshold, indicating that the battery needs charging. If this system has failed, then either the charge system is on all the time (which is bad for the battery) or off all the time (which will let the battery run down and go flat).
Note that it is common for the charge circuit to run at 100% duty cycle right after starting the engine, because the charge state of the battery will be slightly depleted after a start. Then after several minutes of charging, the charge circuit will begin intermittently cutting out as the battery comes back to full charge until at equilibrium, the system voltage will jump momentarily up to 29 and then jump back to 24 for a while, then spike briefly at 29, then go back to 24, etc. indicating that the battery is once again fully charged.