OP, IMHO one can go nuts reading a myriad of opinions on the subject. I tend to be a research hound, and honesty the mostly well-meaning people that voice opinions on sites like this are great, but it was also over-whelming especially when I spent nearly 3 months reading, re-reading threads, and thinking about converting from ICE, and in my case 10-years of also driving Lexus Hybrids. If a had to be a PhD to understand lithium-ion characteristics, I (and likely many others) would not buy Tesla, but some like to deal with that sort of thing. OK for them ...but as a new MS owner, where I have landed, and where I'd be if I were in your situation is:
- I'd only use 120V as a last resort. It's extra work to connect and disconnect your UMC to receive perhaps 3-4 mi/hr of charge, and to whoever is paying for the electricity and from an environment perspective, 120V is as inefficient as you can get from a Tesla charging perspective. 120V is what I would use if I had no range left to get to something faster and more effecient, e.g. If I owned a cabin in the middle of nowhere that had only 120V and I was going to be there a few days, that would be OK so I had enough charge to get home or to a Supercharger.
- Why not just plug your MS in at home every time you arrive and have no plan to run another errand that day? That's what I do. I have my MS set so it will begin charging if it needs it at 12 midnight every day, and with the electrical rate plan I converted to, I pay the lowest rates 12AM-5AM, and in theory could recharge my "nearly empty" 90D (wth dual chargers and an 80-amp HPWC) to almost 100% if I had to before the rates go up again at 5AM every day. If you plug in MS, it will never over-charge, assuming you leave your default max charge to say 90% (another point others may give you varied opinions on, but your MS comes with that as the default, and it's what I use)... Of note here, is let's say I leave my MS plugged in for multiple days and don't drive it in-between... MS will bring the charge up to 90% the first night, but it won't start a full charge cycle the next night to only replenish the 1-2 mile vampire loss, and only starts a true charge cycle at some later point... It's proven to be smarter than I need to be. I'm letting the engineers that designed my MS, established defaults that were programmed and delivered as part of the firmware in my MS, who also wrote the Owners Manual, and who are responsible for standing behind the 8-year traction battery warranty that is likely longer than I'll own my favorite toy, to be my guide for the most part...
As much as a technicial guy like myself can overthink things (and oh yes, I have many times), I'm trying not to with my MS for the most part when it comes to this whole charging subject. I don't live in the Arctic or in extremely hot climates like I once did, nor do I park my car at the airport for weeks at a time like I once used to -- all being possible reasons one may want to TEMPORARIALY override some defaults Tesla has, depending on ones interpretation and speculation of Tesla's precise engineering and software/firmware design that only they really know the facts to. IMHO, Tesla is using the Roadster, MS and MX to ease their way into how to deal with volumes more EVs being sold per year when M3 and others come to be. Some of the defaults in latest gen MS/MX firmware didn't exist in earlier gen MS when they were delivered, but they do today as Tesla has learned what is more optimum. I'm sticking with the KISS principle as I think Tesla is trying to design their product for, and how Tesla must want all owners to deal with their EVs in the long term so they can reach the masses -- Keep It Simple Stupid. I plug my MS in when I get home every time unless I know I'm leaving for another short errand later that day. I let my MS manage itself, knowing it will be at 90% charge each morning when I wake up, and only think about charging away from home if I really need it because of extended range... not just because I could plug it in and let someone else pay for the little electrical top-off I would be avoiding while I'm out and about. For the daily range it appears you need, I bet you could operate much like I am, enjoying my MS, and really only thinking about charging and range when I have a road trip planned.
