Tyler, this subject gets kicked around every few months and always results in conflicting views. Neted down they are as follows
1. The voltwatch is mandatory on every plane
2. THe Expanded Scale Voltmeter is the only trully accurate voltage check
3. I've never used a meter and always charge my planes before I fly
4,5, 6 and so on are variations and combos of the first three

So, here is what I think. I have a volt watch on all of my planes. It is the ONLY way to get a dynamic view of the condition of the battery under the load provided by your plane. When you have your radio turned on, the volt watch shows the voltage the receiver is seeing. As you wiggle the sticks and cause more current draw while the servos are moving, you can see the resulting voltage drop on the Volt watch in the form of flashing lights. In short, if you turn on your radio and the volt watch shows full charge and when you wiggle the sticks, the lights go down near the yellow zone, the battery doesn't have a full charge. If you have a servo that is stalling out, you can see the extra current draw when it hits the stops and stays there.

The argument that the Expanded Scale Voltmeter is the only way to get an accurate reading is just an emotional argument. These guys believe that a "cheap piece of electronic junk from China" can't be accurate and counted on. The truth is that the Voltwatches are probably more accurate than the Expanded scale meters.

You are correct in thinking that three flights is to short for the day. I can't tell you that you can get four or five flights because I don't know the capacity of your batteries, the loads you are putting on them, the quality of the charge you put on them, or there condition. It may be that you are pushing the limits on the third flight, or it may be that you have five more flights left. A quick look at the volt watch will resolve that question.

As for flight time. Get youself a "GOOD" field charger. You can top off a 1000ma NiCad pack that is down by 25% in just about 10 minutes. You can either power the charger off your car battery or like I do, off my starter battery. Some guys make sure that they can easily change batteries in the plane and carry a spare. This is another approach, but I would rather charge the battery than change it. Don't forget your transmitter battery. While it usually has longer life charge than the receiver battery, it still needs to be monitored.

SO, either a volt watch on your plane, or an Expanded Scale Volt meter in your flight box. One of these is mandatory.

Don