RE: regular voltmeter and onboard?
I guess it all depends on the application and how much you really want to know about your battery. I have 5 planes, all giant scale 30% +... all on Lithium power. I need a consistent 1A dynamic load, which is what an "active" load places on the pack. A simple resistive load may be fine for one pack type, say NiCads, but wont work very well for a variety of packs like 4 cell, 5, cell, NiMh, Li-Ion, etc. I use the meter for my cars, boats, helis and planes... all on different voltages and battery types! It has paid for itself over and over. The reason that little H9 meter costs what it does is that it provides a 0.5 and 1.0 A load at all common voltages up to 12V using a remedial load circuit - something like a reverse regulator... Its not just a panel meter with a resistor inside.
I at least know that if my pack is at 8.3 volts or 7.9 volts it will hold the load when the meter is connected. That simply won't work with a meter and fixed load (i.e. resistor or light bulb) unless you carry a resistor network or rheostat and just happen to know which value is needed for which voltage. ..
If you look at the pic below, you can see there is a little more to this meter than just the load resistor.. the circuit under the heat sink is the active load.
Anyway, it was just a suggestion. If money is that much of an issue and you are only using a 4-cell NiCad for the rest of your flying days then I guess the meter approach is probably OK...
I tend to heed the old motorcycle racing adage - "if you have a $50 head, its OK to buy a $50 helmet" ...
DP