Um, that sucks, and with the motor down by the head it is bound to get moisture. This is an application that screams for a brushless motor if you ask me, but I guess that's not what what they're using.
Now back to the cost: you've given me some real numbers to work with. Thanks.
What's the cost of that 140 gallons of gas, plus 2 gallons of 2cycle oil, plus a plug, air filter and fuel filter? Somewhere around $600, right?
Based on Richard Martin's charging cost estimate (which looks pretty well thought out to me), and 28 weeks, charging FOUR batteries each, once a day, 6 days a week, you're looking at $12.10 in electrical charging cost.
Four AP80 batteries (forgetting about the cost of the equipment for a moment) run about $600. That's about the same as the first season's worth of gas (even counting the charging cost). So the first year is about break-even.
Now, based on 28 weeks, 6 days a week, you're looking at hitting the 500 charge cycle count in just under three years. By then, they claim you will still have 80% of the battery capacity remaining, but even so, after the first year (assuming you need 4 batteries to get through one day's work), you're no longer paying for gas.
If you get 5 years out of the batteries (not counting equipment failures), you could have saved around $2350 (mostly in gas).
If you can get away with just two batteries to get you through the day, your break even time is cut in half.
Now for me, I'm just a homeowner who is interested in the math for the academic purposes. I've got too much tied up in my Kombi motors.
But if Stihl had a Li-Ion Kombi head that could compete with the KM110 for power, where I could still keep my attachments, and if it were brushless, I sure would think hard about that when it comes time to replace my engine.