Lithium Battery Charging

The recent cold weather has got me thinking. My Symbol was like a block of ice earlier this week and the internal temperature was close to freezing. The outside temperature was only -2 and it had been down to -5 overnight so reasonable to assume that the internal temperature actually dropped below freezing.

If I started the engine then, the fitted B2B (Sargent DX320-12) would start charging the LB at possibly below freezing. 2 questions:- Does this matter and is this why the B2B has an optional temperature sensor? (The manual isn't clear.)

The Sargent B2B charge rate can be optimised by temperature sensing but nowhere does it say that it will not try to charge a Lithium battery in freezing conditions. The B2B is needed when the vehicle has a smart alternator which I believe all new AS chassis now have.

Quality Lithium batteries have an internal BMS that can control the charge rate, and not charging at all in freezing conditions as that would permanently damage the battery. For some, in freezing conditions they will use remaining battery power to use an internal heater to raise the temperature of the battery to a level where it is safe to charge. I don't believe the type of Lithium battery that AS fit as standard has either of these features.

I've not yet heard of an actual case where an AS fitted Lithium has been damaged by use of the vehicle in freezing conditions but I am aware of some unexplained failures of such batteries.....

And if you set aside the possibility of actual damage, there is also the fact that the "cycle life" of an LiFePO battery is reduced by being charged at a low temperature - and it's not a small effect either.

I looked at a LiFePO battery at random (a LiFOS105) and their data sheet shows that the battery's usable life is near enough halved by a temperature of -10, compared with the lifecycle at 25 degrees (1400 cycles versus 2750).

Two other factors have a significant effect: high temperatures (at 45 degrees you can knock the usable life down by almost a third) and depth of discharge (fully discharging the battery regularly takes a not insignificant 60% off its life, compared with only discharging to 50%).

In fairness, though, the number of usable cycles is still very large, compared to any similarly sized lead/acid battery.

I’m going to sound like a right old stick in the mud dinosaur but the more I hear about Lithium, the more I’m just going to stick with my LA leisure battery for now, it does exactly what I want with 160w of solar on the roof and my power consumption is not exactly small.
Don’t get me wrong, I love new technology and I believe Lithium is the way forward 100% but not right now.
Well not the way A/S incorporate it IMO 

Thanks for the replies, think I'll talk to dealer. Should have a BMS I think.

I think a lot depends on the battery, as they aren't all the same. Some will charge down to -30C because of internal heating, others will prevent charging if it will cause damage. And if the battery is actively being charged it may stay above 0C inside anyway. But even if the battery doesn't have an internal heater, and you have mains connected, a heater set on a frost free setting is one way of fixing that. Or a heating pad underneath, with temperature sensor. They are available. Also powering down the EC700 in cold temperatures if the van isn't being used will be enough to keep the charge in the battery anyway. 

As I now have a Sargent DX320-12 B2B charger as well (and an MPPT solar controller before everyone gets overexcited) to ensure that the battery doesn't have too hard a life on my 30 day trips without mains hookup, and to mitigate the unpredictability of the smart alternator/split charge relay, I will replace the leisure battery with LiFePO4 when the time comes. At the moment, I still have the conventional battery, but it is past its best. Maybe another season out of it, though. LiFePO4 are long lasting, lighter, smaller and allow deeper discharge without damage. But they aren't all the same.