I would agree, plus it gives you the option to fill your battery from E7 in the winter when you'll get almost no solar - you should just check that the Duracell battery has that option.I *think* it sounds as though E7 would make sense for us...
At the risk of stating the obvious or of 'teaching grandma to suck eggs':
1. It sounds like you're using a ton of electricity - do you have an opportunity to cut down in parallel with introducing your solar? For example, tumble dryers can take a stack of electricity; you could be taking all day to fill your battery with solar, then emptying in just an hour or so once you put on the tumbler.
2. Try and get your head around units as it all then starts to make sense. Power is measured in kW, energy in kWh. If you have a Leaf that can store 30kWh, and you charge it with 3kW power, then it will take 10 hours to fill. Your Duracell battery can hold 3kWh; if you use it to run a 1.5kW tumble dryer then it will be empty in 2 hours. kWh is the size of the bath, kW is the speed of the water going in or out.