That's extremely interesting and informative, and completely contrary to what I'm trying to do. I like the answers about using the pot on the board to lower the output power. Excellent. I'll probably do that.
But my initial problem was that, with a particular battery pack, the rig overdrove my tuner, making it fail to tune. Thankfully non-catastrophically, (i.e., it didn't catch fire) but it still wouldn't tune, and indications were that the power was out of range at the top end.
I realize that most users of radios want to MAXIMIZE output power, and then level it across as many bands as possible, so they have lots of output power in all of the bands they want to use. But I don't want to increase the power. I want to control it. The battery's specs list it at 12v @ 5A. So it has plenty of power and shouldn't limit the transmitter. But that's not my issue. The issue is that with that battery supply, there's TOO MUCH OUTPUT. If I run it from a bench supply, it doesn't do this. If I power the bench supply from the battery, it doesn't do this. I'm charging a battery bank I have with a 12vdc output jack, with a limit of 3A, that I'm going to test to see what IT does.
But I don't WANT to maximize RF out. I want to keep it within the limits of my tuner. I will try not setting a limit on the amperage and just try lowering the voltage, and see what that does, if limiting the amperage causes Bad Things.
Am I not being clear as to my goal in this instance? I'm trying to assemble a portable setup to take into the field for battery operation, but everything needs to play nicely with everything else, and the battery I was trying wouldn't play well with the tuner. I'm also testing to see if the problem might have been with the antenna or with the tuner, by testing different antennas and different tuners, to see if the problem actually exists with the BATTERY and not something else. If I can do it with a different battery pack that doesn't overwhelm the rig, PERFECT. But if that's going to cause bad harmonics or spurs or splattery signal, then that's not so perfect. I want to find the actual CAUSE of the difficulty, not just slap a band-aid on it or treat symptoms, but so far the assumptions I keep hearing are that I'm trying to maximize output, which is not the case. If I wanted to maximize output, I'd be building different sorts of radios, not QRP rigs.