I have 2015 rMBP and its hooked to a thunderbolt display and uses it's power cord for charging. I noticed that the charging wattage is really low(~2W) compared to what I see when using the MagSafe 2 power adapter(~54W). The wattage actually fluctuates when using the thunderbolt cable. So just wanted to know if this is normal? Or is there anything I can do for this? Would I be damaging the battery this way. I really don't want to use the MagSafe adapter because of how the cables are setup now. Thanks in advance for your help!
Best Answer
What you are seeing is the "current draw" for charging the battery. This will fluctuate and is perfectly normal.
You will see this fluctuate more so when the battery is full or nearly fully charged when it doesn't need much current to bring it back up to 100%. When it reaches full charge, there's no need for full current draw.
The 2015 rMBP has either a 60W or 85W power adapter (13" or 15" respectively). 54W draw is well within the limit of either adapter which means (to use a Star Trek: TNG phrase) it's operating within normal parameters. The 54W is just the draw at this particular time; charging the battery and powering the MBP. Crank up some processes (like video editing) and your draw will go up. Turn it off/put to sleep and ~100% of the power will go to charging the battery until it's full.
There's nothing to change nor is anything here harmful to your battery.