My research seems to indicate that the biggest thing that impacts battery lifetime (lifetime defined as runtime approximately 80% of what it is new. For us, estimated or ideal range after a charge) is depth of charge with 90% depth of discharge (DoD) resulting in about 50% lifetime compared to 10% depth of charge for LiOn cells. My calculations indicate that if you could live with 10% DoD you would probably get 160000 miles on a pack (assuming all good cells) and if you needed 90% DoD you would probably get 80000 on a pack.
My research also indicates that the charging amps doesn't significantly impact battery lifetime (Subjective what that means, but something like 2000 miles on 80000 miles, which to me subjectively, is not significant enough to drive any decisions about whether or not to use lower amperage. To others, 2k on 80k miles can be significant.)
From a what you pay to the power company standpoint, I currently only have 120V circuit and until I can get 240V installed (soon I hope) I can say that I consistently use about 9kWh per day driving (usually about 80% SOC when I start charging, for about 40m commute with the Roadster) and when I charge, VDS consistently shows that it is costing me 17kW to get back up to 98-99% SOC on a standard charge in about 10 hours. To me, this means that the PEM and fans on the Roadster that are continuously in use during charging consume about 800 W/h to do whatever they do. So, to me, it seems that each hour that you reduce the time that you spend charging, you save paying for 800W/h to the power company.
My research and analysis also indicates that charging efficiency increases until you get up to about 32A, then it decreases, but not that much, so there's not a huge cost penalty if you need to charge faster but it is a little less efficient.
I just purchased my Roadster about 3 weeks ago (#543) and I'm getting a second estimate from an electrician for 240V this week. I've purchased UMC (which is limited to 32A) and CAN SR, and I'm asking for quotes for 50A and 100A circuits with 50A breakers. I don't (think that I) need the 70A that car can take, but if it doesn't cost that much more to install 100A wires (2-3 gauge vs 4-6 gauge. I need an 80 ft run from where the power enters my house to the garage) and if I have the right wires, I can later change from UMC to HPWC if I change my mind about how long I want it to take to charge by just changing the breaker.
If I have the bigger wires and circuit capability, I can decide later, easily, whether I want to upgrade to HPWC and charge more quickly. If I don't have the bigger wires, I'll need to get new wires run at that time, if I decide that I want to charge faster.
At present, I typically drive 40m per day back and forth to work, which means that even with 120V/15A, I can fill the 20% SOC that I use overnight (10-12 hrs). With 240V / 32A, I'll be able to that in 2-3 hours or do a full standard charge from about empty overnight. So, if the premium for 100A circuit capability, isn't very much I'll pop for it. But if it's a big step up, due to the more difficult challenge of running 80ft of 2-3 gauge wire, I'll skip it, since my driving habits don't really need the extra (and... 32A seems to be optimal for maximizing charging efficiency and minimizing payments to the power company).
In short.... figure out what you subjectively need or want and is best for you and do that, but don't worry too much about what is best for the battery.. but, guidelines for being nice to the battery:
1. charge as often as is convenient (minimize depth of charge)... per manual, plug in when not driving.
2. charge as slowly (lower amps) as is needed to meet whatever you need to do (maximizing battery life may or may not be your priority).
3. If you are adding new circuit anyway, make it as large as you feel like paying for. If you have the higher capability, you don't have to use it.
4. If you can't get the biggest, for whatever reason, don't sweat it. Most likely it won't make any difference, unless you drive a lot of miles per day, or never sleep and need to drive 24x7.
Enjoy the car...... that's what it's about.
