Cappa, your Tx doesn't use the flat pack, I checked for you.
Here is the battery your Tx will come with:
http://www3.towerhobbies.com/cgi-bin...?&I=LXLV15&P=V

So this is the proper replacement:
http://www.all-battery.com/index.asp...ROD&ProdID=166

The charger that comes with your radio will charge both replacement batteries (Tx and Rx) but it will take 21 hours for the initial charge (your wall wart charger is 150ma output). You can use your multiplex and do them one at a time, at C/10, for 14 hours each for the initial if you wish. The amount of energy you will use in a day will most likely be replaced in a good 12 charge with the wall wart, if you are flying again the next day. If it is not fully recharged in the 12 hours, you will still have PLENTY of juice to fly again, or you can peak each battery with your computer charger the morning of or at the field.

Again, I have the same capacity battery packs and use a wall wart for most of my charging, peaking the batteries once in a while with my computer charger. This works perfectly.

Edited: The wall wart charger that comes with the Futaba 7c radios has an output of 150ma Rx, and 170ma Tx. This would charge a 2300mah battery in 21 hours (2300x1.4/150=21)