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 * 20ah = 960wh. 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 960wh / 20w = 48hrs.
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