Version 2.05 has several power options:
1) 6-42V switch-mode PSU. Suitable for automotive or battery use. This is very versatile and will work happily with the nasty power you get in an automotive envionment. This option is not fitted on most of the boards shipped so far - you can tell by looking in the area in front of the Compact Flash socket on the back of the board. If you have a max629 IC, an inductor, and 4 big tantalum capacitors here then this is fitted. The 2-pin connector to the left of the CF socket [(J17) | http://www.balloonboard.org/hardware/205/con/battery.html] is where the power goes in. +VE is the pin furthest from the big expansion connector.
2) 5V supply. If you have two max894's fitted (between the ears of the compact flash socket on the rear of the board), then you have an onboard 5V->3.3V regulator fitted and can supply the board with a single 5V regulated supply. Some 2.05 boards have this option fitted - some don't - check before powering it up! The 3.3V and 1.8V supplies are generated from this. This chip has a 500mA limit so if you fit a CF card that uses 3V then it is easy to overload this supply: if you get unreliability consider this possibility. v2.06 will be upgraded in this respect. The 5V supply is used directly for Audio, USB power and LCD bias voltage. 5V is applied to the rightmost of 3 holes in the top right of the board marked '5V'. 0V to the leftmost, marked '0V'.
3) 3.3V supply. If you only have one max894 fitted (see above 5V description), then the board needs to be supplied with a regulated 3.3V supply. The 1.8V is generated from this. The 3.3V is applied to the middle of the three holes in the top right of the board, marked '3V', and 0V to the leftmost, marked '0V'. The board can be used like this, without 5V but functions needing 5V will not work (audio, USB, LCD supply). You can supply 5V via the '5V' hole for these functions, if required, and might want to do this for efficiency reasons, because the max894 is a linear regulator and thus not the most efficient possible option. The 2.05g variant is normally supplied in this form.
NB: The 5V Supply isn't always required to power the LCD as far as I can tell. It is, however, required to power the -ve bias voltage generator, should your LCD need it. Thus, it will depend on your LCD as to weather you need 5v to run it or not. The LCD interface I'm working on for the Aleph LCDs ([BalloonLCDInfo]) will use the 5v supply for convenience with prototyping and to avoid overloading the 3.3v supply. (Peter Clifton)