For field trips I use a Celestron Powertank 17 which seems to last for ages. My current Powertank is a warranty replacement for one I bought at the SPSP some years ago. The original one just wouldn't hold charge however the current (no pun intended
)one is superb.
At home I use a Powertech regulated power supply (Model HW1200R-12) which was obtained from Jaycar for around $60 - $70. The output of the power supply is 13.8V DC and is rated at 12 amperes. I suppose the box is around 170mm x 160mm x 75mm and is fan cooled. As the gemini runs between 12V - 18V this is an ideal power supply and has never giving any problems. As for the power lead, I found it impossible to buy a 4 pin DIN plug anywhere so I just bought the standard power lead (DIN plug/cigarette lighter adaptor) from ATS and cut the cigarette lighter adaptor plug off it and soldered the required 'push in' connectors to it.
Hope this helps.
Cheers, Steve