If your transmitter has the older style battery connector it will be just like the one on your receiver. If that's the case you could use the voltmeter, but the battery indicator on the transmitter is pretty good, and you don't have to worry about a "servo load" on the transmitter pack, so I wouldn't use it. (The voltmeter puts a false "load" on the receiver pack to determine if the pack has sufficient capacity, not the case with the Tx.)
Dennis-