Depends on how much current your motors need, especially during starting. You may find the charger goes in to current limit. The charger voltage will be slightly higher than the battery voltage so the motor will run faster. Some chargers have lousy voltage control when they are off load or at very light load - don't kill your control electronics.
Why not just use a standard power supply?
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If we learn from our mistakes I'm getting a great education!
Not all battery chargers can be used as a power supply. Some chargers have little or no filtering, they use the battery as the filter. If the charger is not a "battery elimator" there may be ac ripple on the output of the charger.