How long aprox will a stand alone car battery last if used only for charging mobile phones?
Here’s a short answer: you should not have any problem at all charging 10 mobile phones daily for a couple of weeks. Here’s the long answer: Using my blackberry Curve 8330 as an example the battery is rated at 3.7V and 960mAh. The equation is Watts = Volts * Amps. For simplicity sake, let’s just use 1000mAh or 1Ah. This means that the battery needs 3.7watt hour of energy to recharge if it were completely dead. Next, let’s assume your standalone battery is rated at 500Ah. 12V times 500Ah = 6,000watt hour or 6.0 kilowatt hour. Assuming no energy loss, your standalone battery can charge about 1600 cell phones. Here are a few caveats. Recall that both the car battery and the cell phone are DC devices. If you were to use an inverter to convert from DC to AC and then use a house charger to convert from AC to DC, then there will be some energy loss. A reasonable guess would be about 20-30%. If you also plug a power strip into the inverter, then there will be further power loss. To avoid these
