I agree. It's battery temperature that determines when and if they will receive a charge. Permanent damage can be done to the batteries if they are 'force' charged when cold. A small 'leak' charge is intially put through to warm them first, in readiness for full charge.

If the battery pack cannot accept charge when it is cold, how is it that it can deliver charge when it is cold?
Just got my 06 HCH this summer, so I have no winter experience yet, but already on cool days (even above freezing) I go 5 mins before I can regen. (Haven't tried shifting to S yet. I'll try that, but it gets the revs up.) Once it's warmed up a bit I can sometimes trick it to regen but giving the gas a jab and release, and then touching the brake as soon as I see one green bar after the release; though I'm not sure that this will actually save me anything overall unless I'm going to touch the brakes for a good distance.

Are we sure that there is a temp sensor in the battery pack as well as in the motor? Sounds like a block heater will help, but I'm also considering an interior warmer. Maybe an interior warmer in the trunk would be more effective than in the cabin...

I have a block heater in mine, it helps a lot, just put it on a timer so it only runs about 4 hours anthing more than that I found to be a waste.

there are several temp sensors all over the IMA system.

RE: small 'leak' charge is intially put through to warm them first...
Does the engine have to be running, or can I just turn the key to on the get the leak charge going and wait for 5 mins like that?

RE: block heater. Yeah, I'll try it. Don't worry - I have a timer. Luckily I also have an attached garage, so it's a bit warmer in there and out of the wind.

It is normal for the HCH not to regen or A/S until it has warmed the ICE.Normally about 5 min. You can make it regen early by dropping into drive two when slowing down. H

The leak charge is coming from the engine.... thats what warms up the battery. If the engine is off there is no way the battery is going to be taking a charge unless the vehicle is moving and slowing down... which is regen and that isn't happening because the car is cold.

So... yes the engine has to be running... and there is no point in just sitting there because that will just burn gas to no purpose.