Charge the TX full up overnight.
Next day, Turn the TX on, grap a bag of chips, a frosty beverage, slip a DVD in, & watch a show.
Every 10-15 mins look at what the voltage is.
After a while, hopefully a long while, the TX will say it's had enough, and start beeping the Low Voltage song.
That will give you a good idea of the condition & life of your batteries, and will help us see what problem if any you have.
(this is for a digital volt meter, not a needle type)

When my TX stops saying over 9 volts, I stop flying. But I leave it on at home to complete the charge/drain cycle before recharging.... sometimes a half hour or more before it beeps. Some folks stop at 9.6, some stop at 9, some at 8.6 - but seems to me the TX itself is set to tell you LOW VOLTAGE from the factory. I doubt they intentionally set the warning 20minutes past safe transmitting.