In either case, EGO's battery and charger systems are the best on the market anywhere that I've seen or read about. There have been some reports of defective batteries/chargers but all batteries/chargers are bound to have a few that miss quality control and so far I've read that EGO stands behind their batteries/chargers and will readily replace defective units.
Lithium-ion batteries in general have a very good shelf life from all that I've read online. But waiting for Spring will add several months to the 3 year warranty if you wait.
Either way you're going to happy with a mower that needs NO gas, oil, oil changes, mess and recycling, spark plugs, air filters, tuneups, priming, pulling on the cord over and over to get started and hearing protection. You definitely will like the ease of starting, changing cutting height, swapping batteries, fold-up storage, removing and replacing the grass clipping bag, lack of exhaust fumes, its light weight and maneuverability.
Good luck with your choice!
Gut feeling is we'll see a new model this spring, also an edger (I would rather see the edger first). But of course I'm speculating. Either way, storing this mower over the winter will be just fine. After your last cut, charge your battery half way and store in the house, in a closet, or anywhere that the temperature stays pretty steady and even. 60's to 70's. Li-Ion Battery's should not be stored at an empty or full charge state (so the chemists say).
This mower and the other EGO tools have saved me a lot of time and headaches this summer. I got really frustrated with my gas trimmer and the spark plug filing. Endless mixing of gas and oil for other tools. None of that this summer with the EGO stuff. Grab a battery and off you go.
Best of luck