Is There Any Way to Charge a 24-Volt Battery From 12 Volts?
Electricity is measured in volts and amperes. Voltage is the pressure of electricity that flows through the cables or wires. A good comparison is the pressure of water that comes from your taps when you turn them on: The greater the pressure, the more force there is and the faster it flows. You may use a 12-volt charger to charge your 24-volt battery, but it takes a lot longer and your battery will need charging more frequently. Alternatively, you may wire two 12-volt chargers in series to produce 24 volts.
Single 12-Volt Charger
Attach the cable clamp on the end of the black cable from your 12-volt charger onto the negative terminal of your 24-volt battery. The negative terminal is labeled "-" or "Neg."
Attach the cable clamp on the end of the red cable from the 12-volt charger onto the positive terminal of your 24-volt battery. The positive terminal is labeled "+" or "Pos."
Turn on your 12-volt charger. Leave it to charge for at least double the time you normally charge it using a 24-volt charger. For example, if it usually takes six hours, let it charge for at least 12 hours.
Two 12-Volt Chargers in Series
Wire the chargers in series by connecting the black clamp to the red clamp.
Attach the clamp on the end of the black cable from the first 12-volt charger to the clamp on the end of the red cable from the second 12-volt charger.
Attach the clamp on the end of the red cable from the first 12-volt charger to the 24-volt battery's positive terminal.
Attach the clamp on the end of the black cable from the second 12-volt charger onto the negative terminal of the 24-volt battery.
Turn on both 12-volt chargers. Let your 24-volt battery charge the same time as if you were using a single 24-volt charger, then turn off the charger.