If it were me, I think I'd hook the battery packs up to three 12 volt lights in series and put an ammeter in series with that also. Then I'd stick a video camera in front of it and walk away. Sometime after the light went out I'd check the video to see when the light went out. That would tell me I could draw X amps for T amount of time. In other words, it'd measure the actual aH at that particular current draw.
For even more info, I'd put a voltmeter in parallel with the load and make sure the camera could see it. Then by reviewing the video I could plot the voltage drop over time.
If you did that to lithium batteries, they would never recharge again, and would probably explode if you tried. That's IF you could get a lithium charger that would actually try it. Mine wouldn't. You can't discharge those below 2.8 to 3.0 volts per cell (depending on the type), or they don't come back.
I wish you guys would relate your packs in terms of cells in series. A "48v" pack should be 12S (12 in series, the other part is "P", for parallel, so if you had 6 cells with 2 in series, and two each, sxs, it would be 3S2P), which, @ 4.2v per cells comes to only 50.4V, I think 52v is too much. Most of the cheap chargers are dumb, and only have a peak voltage limit. It would be fine if you have some kind of protection circuit, which you should, but I don't. I have a 10S2P pack on a 36v system, and my cheapo charger just stops at 42v. It blinks on and off for a while near the end, but that's it. 50v would be fine for a 12S pack. Particularly if you are using cylindrical cells. My smart charger has a setting for those that only charge them to 4.1v per cell, although all the other chargers will make them 4.2. My smart charger also has a discharge function that will discharge them to the safe limit, and measures the actual aH, like you wanted to do the hard way.
BTW, that's a $25 r/c charger called a B6, which is a great machine, but it only charges up to 6S, which is why I have a dumb charger for my bike. The B6 will recondition nickel packs, too. It requires a substantial d/c power supply between 11 and 18v, it's meant to be connected to your car battery, at the r/c field. If you get into lithium batteries, a good smart charger is a wise investment. I made a report on lithium battery types I posted on another forum, but I'll copy it here, just FYI