How to read car charger input current specification? I found two MacBook 60 Watts car chargers, one says on the backside “INPUT: 12V-24VDC 5.6A MAX”, the other “Input: DC 11-15V Max 10A”. So, the latter has an efficiency of 50%?

http://ecx.images-amazon.com/images/I/619ISd6fcKL.SL1500.jpg

http://ecx.images-amazon.com/images/I/61qLRTluyUL.SL1500.jpg
No, you have to read the description different:

#1) Input 12-24V means it is capable for normal cars (12-14V) and Trucks (24V) and the 5.6A Max. is most likely the maximum allowed current before the internal fuse blows off.

#2) Input 11-15V means it is only usable for cars (no Trucks) and a maximum current of 10A before the internal fuse blows off.

so ... they are both usable for your need unless you own a Truck, then you should take #1.