Battery life is unaffected between L1 and L2 charging on the Volt because the L2 charging limit of the Volt (~3.3kW) distributed across all of the battery cells is still well under the threshold for decreased battery longevity of lithium-ion batteries. In hot weather, the TMS is undoubtedly essential for safely charging the battery at L2. In the Canadian winter for example, I strongly doubt that the battery would need any cooling even during an L2 charge...heck it might even need some heating!
2012 Volt #C6688 Silver Ice Metallic (GAN), Premium Leather Seats with White trim (AFD), Bose Speakers (UQA)
Placed order June 28 2011, built October 11 2011, drove home November 4 2011