batteries

You say the separate controller battery can't output over 13 volts. This leaves out car/MC batteries that can sometimes be 14 Volts or so. Any suggestions for a good controller battery?

This is actually only true if you own an earlier version of the AX2550.
Since early 2004, the Power Control input feeds into the DC/DC converter (via a diode) and can accept input voltage up to 40V. Look the the PCB version written on the sticker on the back of your unit. If 5.2 or higher, it will accept the higher voltage.

Until today, we have not revealed this change in order avaoid confusion between the earlier and newer units.

We will be updating the manual to explain the change.