I'm actually pretty skeptical that this is really necessary or beneficial. Even the charger for a $100 cordless drill has enough smarts to hold off charging a hot battery. I'd be completely flabbergasted to learn that the charger for a $30,000 PHEV doesn't do that as well.
I wonder... Whether you are designing the charging system for a cordless drill or for an automobile, it seems to me that your primary goals are to prevent the battery from heating to a point where it catches fire, and to ensure that the battery survives its warranty period. Beyond that, it's likely to be difficult for the design engineer to know where to "draw the line". One person might plug in their drill (or car) and want it to begin charging immediately so they can use it in an hour. Another person might not want to use it until tomorrow and given a choice, might have a strong interest in delaying charge until cooler temps prevail in order to maximize battery lifetime. Just for the sake of discussion, lets assume that the design engineer believes that if they prevent charging above 120 degrees F, then the battery is likely to be safe and to survive its warranty period, just barely, but if they prevent charging above 100 F, the battery is likely to survive its warranty period by two years. If they choose 120, they'll keep the "want it in an hour" person happy, but the "want it tomorrow" person's interests aren't well served.
Responding to the original question in this thread, traditional lead-acid batteries benefit from a small "float charge", but there's some reason to think that this might not be good for Li-Ion batteries
. This raises an interesting question: if you leave your car plugged in for an extended period after it's fully charged, how does the charging system respond to that? Does it shut down and stay down? Probably not: at some point the parasitic load is likely to reduce the charge to the point where the charger begins charging again. That's probably not a big deal when the battery is new, because when the battery is new it's not being charged to 100% of it's designed capacity. But when the battery gets (considerably) older and the BMS starts allowing charge to approach 100% capacity, perhaps it's better to disconnect after the battery is fully charged, or at least put the charger on a schedule that causes it to shut down and stay down.