I've read lots of threads on RCU saying you should run a 6 volt pack with Spektrum receivers.

One option for a 6 volt pack, $20 with your choice of connector. Sanyo 1700 mah cells.
http://www.cermark.com/products/Sany...00MAH-AUL.html

Here is a link to a switch harness with charge jack that should work fine.
http://www.cermark.com/products/JR%2...ging-jack.html

You can get a wall wart charger, for 9 bucks, that has 125 mah output to charge a decent sized pack overnight.
http://www.cermark.com/products/CHAR...-125-MAH.html#
You can buy "smart" chargers, cyclers, etc, (a lot more than 9 bucks) but this one will work for basic needs