Capacity or length of time a lithium battery will last is based on the WH (watt hours) of the battery which is Ah (amp hours) multiplied by V (volts). 48v * 12ah = 576wh. The length of time the battery will last will be measured by the W (wattage) of the device using electricity. Ex: Running an RV Fan that pulls 20 watts would last 576wh / 20w = 28.8hrs.
Give our support team a call if you would like help calculating the battery capacity you may want for your specific needs. (657) 215-1256