Thanks all.
I bought this and also the Hobbico Mk II expanded scale voltmeter. When I tried it, I had some strange readings and maybe someone can help with them. With the antenna down my transmitter was showing weak but with it up the need on the Mk II showed max power. However, this has not been charged in several weeks. As a matter of fact, the radio was reading 9.3 V and after several tests of servos for a FourStar 40 I'm building, the radio started beeping and the voltage was showing 8.8.
Maybe I didn't have the leads in right, but testing again showed the correct reading.