We used a dc-dc laptop charger with an anderson connector on it
at SVR. The one problem we did have was that our 110 volt classmate
charger died on Friday, we would have been up a creek without the dc-dc
charger. We used it to charge the laptop overnight on Friday night,
putting a fresh battery on it when we left the pits at 6pm. We then
used it all day on Saturday. It worked out well for us.
The 20 volt, 3.7 amp charger with the 5.5mm-2.5mm plug at
www.powerstream.com is ED1075-52. RadioShack
has a very cheap universal one with lots of plugs and adjustable
voltage, but you will have to check the plugs it has for a proper
fit.
Eugene