The comments of an electrical engineer would be useful here (hint, hint), but an interesting article states if properly used, our high voltage batteries could last 15 to 20 years:
Expert: What You Know About Lithium Batteries Is Wrong, Can Last Up To 20 Years | Inside EVs
The article is from 2013, which would correlate well with the battery technology inherent with 2013 batteries that many of us have. Mikael Cugnet, a battery expert with the French Atomic Energy Commission offers these tips to extend battery life:
1) avoid high heat (e.g., leaving the car in the summer sun for extended periods). That's good news for those of you in Canada! Those in warmer climates may want to consider a car cover to shade the car when parked in the Sun for long periods.
2) Too many fast charges can damage the ability of a lithium battery to hold a charge over time. Thus, if you have the time, use your 110V charger overnight.
3) Lithium packs that are only charged to 50% of capacity will last the longest. Ideally a charge should stay between 20% and 80% of total capacity. Thus, unless you plan on doing a long drive the next day, don't charge it to full capacity.
4) An onboard active cooling system, such as the ED has, is a big assist to battery life. Thus make sure your cooling system is functional.
I suspect you could actually get more years out of your battery, but at a reduced capacity. I suspect (again, the advice of an electrical engineer would be useful) that if the battery drops below 80% original capacity that you can still drive your ED just fine. Everything should still work; you just can't drive it as far. MB of course guarantees 80% of more of original capacity out to ten years under BAP, but I suspect if you drop below 80% after ten years that you can keep driving the car with reduced range. Thus, if you are like me and just use it for short trips around town, you could conceivably get 30 years of use or more. No need to purchase expensive replacement batteries.