This might be a silly question, but does the amperage matter when charging, if you wanted to maximize the life of the battery? Does trickle charging it with the spare mobile connector (15A) work better to extend the life, than using the 30A UMC? My commute to/from work is about 70 miles a day. If I plug in as soon as I get home from work with the spare mobile connector, I will have a full standard charge in about 14 hours. That works out perfectly for me. Just wondering if that is better than 30/40A charging.
Even charging at 240V/70A (16.8 kW) is very nice to the Roadster's battery. To gauge the level of charge, divide your charge rate (in kW) by the pack size (in kWh). This is the "C" value for the charge rate. For lithium ion, staying below 1C is considered good for battery longevity. 16.8/55 = 0.3C. That's already so far below 1C that it's not clear there's a measurable benefit for lower charging levels.
Martin Eberhard says Tesla chose to stay below 0.5C for the Roadster.
A Bit About Batteries | Blog | Tesla Motors
By comparison, Supercharging an 85 kWh Model S at 135 kW is 1.59C.
Still, I like slow charging the Roadster because it's nicer to the grid and maybe a tiny bit nicer to the battery pack. For the Roadster, higher charging rates are more efficient. I charge at 32A because that's the slowest I can charge without giving up efficiency, and it's still much faster than I typically need to get a full charge overnight.
Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog
Charging at 120V is not only much less energy efficient, it causes the coolant pump to run much more than with faster charging rates. There's anecdotal evidence to suggest that owners who normally charge at 120V go through coolant pumps pretty frequently, like 3 replacements in 5 years. Our coolant pump died after just over 5 years and 42,000 miles with most of our charging done at 238V/32A.
Having Tesla replace the coolant pump costs $400 for the pump and $300 for labor. You can buy the pump online for $100 (Bosch PCA 12V Part number 0 392 022 002), but I wouldn't let anyone but a Roadster service tech do the swap because you have to bleed the air bubbles out of the coolant lines. It's not difficult to do, but Chris at the local garage probably isn't going to know how to do it. I don't know if Tesla will install a pump that you bring in yourself, but if you happen to know a former Roadster service tech...
The connector to the pump can go bad after years of use. I think I have the part number for that. I'll post that, too, once I've confirmed it. It's an inexpensive fuel injection connector, $12.50 on Amazon, but I'm sure Tesla will sell you one for much more.