which product can I use to power my sump pump
Want to have 4-8 hours of run time for my 1/3 HP pump.
This would be controlled by the amount of times your pump kicks on during that period. That would vary based upon the water table in your area and rainfall. There are DC sump pumps available that will run on a wet cell (car 12volt) battery. That would be a more efficient way to handle your requirement. The pump would always run off the battery and you would use a car battery charger to keep the battery "topped off" and to recharge it fairly quickly if you do run from the battery for a long period of time. If you are subject to frequent, extended outages you might want to consider a deep cycle, marine battery.