Provided most of your contacts list doesn't use whatsapp ... Whatsapp has become so commonly used that my Message app is soon to become redundant. I know it's a matter of opinion but I lol when people suggest to sacrifice data in lieu of better battery life. Might as well don't get a smartphone. Or get a cheaper smartphone that has all the basic smartphone features. They generally consume lesser power. But noooooooo, people want the latest. Even if it means turning off data.

Having a spare charger in office or a car charger would seem to be the most practical solution instead of turning off data, wouldn't you think so?

In my case so far, I have the cable in the car for those "in case" moments. But my usage so far have allowed me to use from 730 am - 11pm with still about 20-30% left.

But I do agree with it in some sense. The car alternator already lots of loads and the spike in wattage each time the radiator fan kicks in. Even worse when air cond compressor/fan kicking in and out as well. It doesn't produce a steady current to charge it properly.

After updating to 6.1.2, massive improvements to my batt life. Yesterday I got 6 hours of usage, 1 day + 9 hours standby when it reach 4% batt life. I'd say a good 30% improvement.