RegGuheert said:
Volusiano said:
So the difference is not because GM hid the capacity information and Nissan didn't. The difference is because GM has TMS to slow down capacity loss while Nissan doesn't.
This is where we differ. While I agree that TMS is needed where you live, I also believe that the battery in the Chevy Volt would degrade FASTER where I live since the TMS buys us very little, but the smaller battery would receive a higher DOD on each trip we take. TMS is not a cure-all.
Reg, interesting discussion. While it's reasonable to assume that GM is gradually opening up the usable battery capacity range in the Volt, the driver community unfortunately does not have access to some important pieces of information, which makes these discussions so contentious. I agree that the LEAF is likely the better choice for your use case. That's why I selected it also, even though I nearly traded it for a Volt when I struggled to make it work due to lack of charging infrastructure. I even made the same assumption that a TMS would not add any value at my place of residence. That said, I was surprised to learn that calender aging was the main driving factor in capacity loss. This is where a TMS or a sensible cooling arrangement in the garage could help.
One of the Phoenix owners had a swamp cooler in his garage, which he installed when he drove another EV in the past. He lost the first capacity bar after 16 months, when most reports seem to indicate that about 12 months were to be expected for 2011/2012 LEAFs in Phoenix. This is very anecdotal, but it does seem to support the notion that a TMS can effectively slow degradation. Degradation wouldn't be zero with a TMS, obviously, but it should progress slower. That said, it's difficult to estimate the impact of calender aging and cycling on a battery without a proper lab test. All the manufacturers have done that, but they are not sharing enough data with their buyers and drivers to allow a qualified comparison of the longevity and performance of these batteries.
While it could be argued that a TMS in a particular climate would slow aging by 30% or 50% (I picked these are numbers from thin air), it's difficult to compare batteries based on their basic chemistry. LG could have made some tweaks to the electrolyte in order to make the cells more heat-resistant. They are already reportedly using a hard anode, instead of graphite powder, which should help improve cycle life according to Charles Whalen. Volt's TMS was carefully designed to keep temperature gradients across each cell to a minimum. There are other interesting design decisions they made, the list goes on. While it's difficult to estimate the real-world contribution of all these factors, it's probably not fair to say that the Volt is only doing better because GM masks capacity loss. It's likely a combination of factors, which you acknowledged, I believe.
My point is that it's difficult to make these comparisons when shopping for an EV or EREV. The batteries could have sufficiently different behavior, even if their basic chemistry was identical. The TMS, while no silver bullet, likely does help slow degradation noticeably, at least at the beginning of the life of the vehicle, when calendar degradation drowns out cycling losses. I don't have much data to back this up, but I believe that Nissan did not include a TMS to keep the cost down. That and perhaps gain more space for passengers. They likely simulated different climates in their lab, and determined that a ten year of life can be expected from the battery. This is likely when the average degradation figures were determined also. This does not mean however, that a driver in Phoenix can expect the same results like someone in Seattle or in London. Unfortunately, it appears that a lot of this information was lost in translation.
Edit: I see that drees and dm33 have already said most of the things I meant to address in my post, and I agree with them.
