Battery chargers (power supplies to use your term) need to be hooked to a battery. The battery acts like a buffer and absorbs current
spikes caused by motors starting.
You said that you don't want the batteries charging/dischargiing if you leave them connected. That won't happen except for a necessary fraction of a second to start a motor
. If the charger output is greater than the electrical
demands, the batteries will never be discharging. Also leaving a modern 3 step charger hooked up to batteries will not harm them.