"some of the batteries may be a little shot"?
is that like being a little pregnant? either the battery's cells are good or are bad.
the battery is the counterweight and the forklift NEEDS the weight for offsetting the weight of the lift.
also, a forklift lifting a capacity load will use almost 500 amps and what ever is the normal battery's voltage, so a 36 volt forklift would need an inverter/transformer of 36vX500amp=18000 watt inverter.
but any DC power supply of the correct voltage and enough amperage could be made to work. especially for the drive function since it does not require the counter weight of the battery to operate.
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