I have one of these transmitters and have used old 1300 Nicads without real problems. I have a couple of times left it switched on for over an hour and sweated whether it would last the days racing. They did.
If you have a Lipo Charger then its worth getting a Lipo 3S battery. I spoke to someone who has one and he said he only needs to charge once a month despite racing every week.
Hobbyking do Tunigy low drain 3S Lipo for transmitters
Turnigy 2650mAh 3S 1C LLF Tx Pack (Futaba/JR)
I bought one and works a treat takes about 10 days delivery ~£14 including delivery. also lighter than NiMh, No more worry about battery on the day
The Argos batteries should last a lot longer than 10 mins and you should not need to discharge them