Wouldn't the battery voltage be the controlling factor here? Probably could go with 2 12v batteries in series? I assume a 20v laptop charger is fine with that.
You really can’t assume much of anything here frankly. Voltages here are nominal, and open circuit voltages can be quite high, or when under load can drop quite a bit. MPPT charger will attempt to maintain and output voltage within it’s target range, but voltage transients and ripple can be a problem - they aren’t designed as a live power supply, they are design to charge huge energy sinks with specific chemistries (aka batteries), so they usually cut corners that would matter in this case but don’t for batteries.