No, I didn't. I didn't have to.

It's sold as a CV charger -- it's designed to deliver a relatively steady voltage at any current up to it's maximum current. What happens above it's maximum current is undefined, but it could 1) keep delivering even more current at the rated voltage, 2) reduce voltage as the current goes over the rating, 3) reduce voltage but hold the current at the rated maximum, 4) reduce voltage and current, 5) simply shut off, 6) release the magic smoke. (If it's a current foldback design, that would be #4 -- a good, safe design.)

If by CV/CC you mean it'll go up to 20 A at 24 V and above that the current will stay at 20 A as the voltage drops to match the load, that would be #3, that's certainly possible, but I don't recall seeing many power supplies set up that way. When I see a power supply that explicitly says CV/CC, it's generally either for welding (and I'm not sure what they mean by CV/CC in that context, but it might be what I just said) or a bench power supply where you can change modes, voltages, currents, etc. (I even have one of those.)

Of course, the spec sheet may very well tell you what happens. That would be part of "knowing exactly what you were doing", but even better is to make sure the current load is never higher than it's rated at.

As for the batteries, if the voltage output of the PS (can it be adjusted?) is the same as their maximum (not nominal!) voltage or slightly lower, that could work. But be careful of what would happen when the batteries are fully discharged and then hooked up -- make sure they don't exceed a 1C charge rate (unless your batteries can be charged faster) and don't overload the charger. If either is true, you might want to add an appropriate resister in series (make sure it's rated to handle your maximum calculated current and can dissipate all the heat it develops!) And a fuse would be very wise. I assume you know all this.

But if the voltage is too high, it'll ruin your batteries the first time you forget to stop it before it reaches that point, and may cause them to catch fire if it's bad enough. And at 20 A, things could go bad very quickly.