Macbook battery information (cold weather & plugged in usage) I kinda have two questions but they're both battery related so I just made one post.

1) Does it harm the battery if I cary my MacBook around with me and the weather is really cold? This has been a very harsh winter with temperatures going even below -15C. Sometimes when I take it out of my bag and then its pouch, it's so cold I can barely hold it in my hands. 

I don't boot it up instantly when getting inside but it's usually sleeping nonetheless so technically turned on. I've read it's a bad idea to start using it since it could heat up too fast and condensate, but is it also harmful for the battery or for the laptop itself to expose it to low temperatures while in a bag? If so, what could be the damage and how can I avoid it?

2) I'm always trying not to use the MacBook while it's charging. Does this matter at all? Should I charge it only when it's sleeping or turned off? How about charging time? Should it be charged only until it gets 100% or I can leave it over night?

Model: 12″ Retina MacBook

Fabrication date: August 2015
If you are carrying the Macbook from outside (cold) to inside (warm &amp; humid), you may want to consider bagging the Macbook in a sealed plastic bag (Ziplock or similar), so the condensate will form on outside of the bag, not the Macbook.

If the Macbook is in a case, a bag, or sleeve, the case should supply some insulation to shield the Macbook from the cold for a short time.

Photographers in cold regions use the plastic bag trick frequently to protect their equipment.

The condensate problem is NOT caused by heating up too fast, it is caused by metal parts exposed to cold, dry air transferred to a warm (relatively) humid environment.  The cold surfaces, like laptop cases or lenses, act as a collection surface for the inside air water vapor.

The Macbook probably has a minimum operating temperature recommendation of minus 5C or so.  

Try to avoid leaving the macbook in a place (car) where the machine will go into a cold soak as to damage the Li-polymer battery.  The battery construction is essentially a layer of foils &amp; gels, and does not take well to deep freezing.  I had a co-worker forget a Windows laptop overnight in a pickup truck, during a -10C night, and the laptop never had useable off-mains battery life again.

Assuming the Macbook has a SSD, the major components susceptible to cold damage are the battery, display &amp; keyboard.

AFAIK, you can leave the laptop charging all the times it is convenient to do so.  The harshest treatment is a daily use of deep discharge cycles, taking the battery to a low state (under 30%), then recharging to 100%, the back to 30% again. 

I'm using a 13" MBP that I travel with, and it shows about 400 battery cycles; by comparison, an at-home 15" MBP, plugged-in almost all the time, shows only 55 battery cycles after more than 3 yaers of use.

It should be perfectly OK to use the machine whilst charging.