Trickle charging 2016 MBP via Dock - OK?

Christopher Kim

macrumors newbie
Original poster
Nov 18, 2016
18
9
There have been a few posts about this in the "TB3 Dock for 2016 15" MBP" thread, but wanted to get a more definitive answer, if possible.

Is it ok for battery health / longevity of the MBP, to trickle charge via an under-powered dock? I have the 13" 2016 tbMBP, and the CalDigit TS3 Lite. I'm very happy with the dock, and knew it only provided 15W pass-through charging for the MBP when I bought it (and thus doesn't advertise itself as laptop-charging).

I use my MBP primarily in closed-clamshell mode, with a 27" LG 4K monitor (via DisplayPort), and only connection out of my MBP is via TB3 to the dock. I am totally fine with the fact that when I use my MBP somewhat heavily, the battery discharges slowly. Given I leave it plugged in the majority of the day/night, it always gets back up to 100% eventually when I'm not using it. I'm totally happy with it, and like that I can use the dock effectively as a 1-cable solution. My only concern is whether this use will at all hurt the health / longevity of my MBP's battery? Anyone have some good info on this? Thanks
 

Brookzy

macrumors 601
May 30, 2010
4,747
4,723
UK
It could arguably cause wear to your battery if you routinely use it plugged in to the dock and no other power adapter because every time your MacBook requires more than 15W it will be drawing it from the battery.

Of course, the battery is designed to be used so this is only a theoretical rather than a practical concern.

It will be fine.
 

Christopher Kim

macrumors newbie
Original poster
Nov 18, 2016
18
9
Got it, thanks. Yes, I am ok with the battery effect of the fact that I'm effectively drawing down the battery a little bit at a time, and then recharging (effectively, it's like using the laptop on battery until it goes down to ~90% for example, and then charging it back up).

My main concern was really if charging the laptop regularly via a cable / power source that isn't the full 65W (ie. equivalent to a 15W charger), is bad for a battery.

Sounds like it's not a big issue...
 

Brookzy

macrumors 601
May 30, 2010
4,747
4,723
UK
My main concern was really if charging the laptop regularly via a cable / power source that isn't the full 65W (ie. equivalent to a 15W charger), is bad for a battery.
If anything it should be better, as less wattage = less heat = less wear.
 

Sanpete

macrumors 68020
Nov 17, 2016
2,123
839
Utah
I imagine this is fine as long as the dock is up to specs, which includes being able to communicate to the MBP how much power it will deliver and delivering only that amount. There have been a lot of USB-C devices that aren't up to spec, and if they end up delivering more power than they're designed for that can be a problem. Hopefully the CalDigit is specworthy.

I'm curious about whether the battery actually charges at all at 15W. I wouldn't be surprised if that power only goes to powering the machine, without powering the battery even at idle.
 

ZapNZs

macrumors 68020
Jan 23, 2017
2,310
1,150
This is a topic being debated among battery gurus - while it will hypothetically interfere with the classic lico charging cycles, the cycles it interferes with should not theoretically harm the battery (after all, multi-charger LiCo/LiMn chargers often have a reduced constant charge voltage when charging multiple cells at once!), but theoretically and actually aren't always the same. :p I sent Cadex an email asking their thoughts on this, as they produce electronic equipment that will likely use USB-C in the future, and are the main group involved with Battery U.
 

Christopher Kim

macrumors newbie
Original poster
Nov 18, 2016
18
9
Hopefully the CalDigit is specworthy.

I'm curious about whether the battery actually charges at all at 15W. I wouldn't be surprised if that power only goes to powering the machine, without powering the battery even at idle.
Agreed, hopefully the CalDigit is spec worthy. Given the great reviews of its USB-C dock, I would think would be okay here.

Re: charging the battery with 15W, can confirm it definitely will charge the battery at idle. The battery runs down very slowly when I'm listening to music via Roon (through external Schiit headphone DAC / Amp connected via USB to the dock, note: the DAC is USB-powered) with my music on a NAS (so constantly streaming) and browsing the internet at same time (all with external monitor via DisplayPort). When idle (or only web-browsing), it charges back up to 100%.

This is a topic being debated among battery gurus - while it will hypothetically interfere with the classic lico charging cycles, the cycles it interferes with should not theoretically harm the battery (after all, multi-charger LiCo/LiMn chargers often have a reduced constant charge voltage when charging multiple cells at once!), but theoretically and actually aren't always the same. :p I sent Cadex an email asking their thoughts on this, as they produce electronic equipment that will likely use USB-C in the future, and are the main group involved with Battery U.
Yes, the battery physics angle is what I'm concerned about, as I don't have a good understanding of how current laptop battery tech works. If you do hear back from them, please let us know. Thanks
 
  • Like
Reactions: Sanpete

aevan

macrumors 68040
Feb 5, 2015
3,119
3,990
Serbia
This is a topic being debated among battery gurus - while it will hypothetically interfere with the classic lico charging cycles, the cycles it interferes with should not theoretically harm the battery (after all, multi-charger LiCo/LiMn chargers often have a reduced constant charge voltage when charging multiple cells at once!), but theoretically and actually aren't always the same. :p I sent Cadex an email asking their thoughts on this, as they produce electronic equipment that will likely use USB-C in the future, and are the main group involved with Battery U.
I too am curious, so share their answer when you get it, please. Thx