ORIGINAL: SushiSeeker
bbrown,
First thing I would try is cycling your suspect batteries a few times. If you don't have a cycler, you can do this with your wall charger a stopwatch or timer and some patience. Fully charge your batteries overnight for at least 18 hours. Then turn on your transmitter and start your timer. When the low battery alarm goes off, note the time. As previously noted, this should be in the range of 3 - 4 hours. Repeat this procedure and see if there is any notable difference.
If you discharge the batteries in this fashion, make sure to extend the transmitter antenna (if it's a 72 MHz) part way so as not to risk overheating the final amps.