I've got a Macbook Pro with 3 USB C ports. I have 2 USB C monitors attached and a charging cable. The battery icon shows it's charging...but the battery still drains. Is the machine confused with all the different connections? Once I unplug the monitors the machine charges normally.
Your computer performs best when connected to AC power. It can use the full output of the Power Adapter AND when doing especially challenging work will also freely "borrow" power from the battery. In some cases, the charged state may even decline during stressful work.
When used only on battery, your computer has no extra cushion of power, and will perform more slowly. However, for ordinary non-stressful tasks this may not be objectionable (possibly not even noticeable.)
In general, you should ALWAYS connect AC power when it is possible to do so, and only run on batteries (which will be somewhat slower) when no AC sources are at hand. There are three micro-controllers cooperating on battery and charging issues, and your Mac will NEVER over-charge.
A charge cycle is ever-so-slightly destructive to batter longevity. When operating as designed (and not using Battery Health Management) battery charge level is allowed to decline to about 92 percent level before initiating a recharge cycle to top up to about 99 percent.
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Catalina software 10.15.5 for MacBook Pro with T2 chip (2016 models and later) includes a new feature called Battery Health Management. Based on your usage patterns, this widens the hysteresis to initiate a charge cycle at a lower level, and stop before 99 percent.
About battery health management in Mac notebooks - Apple Support
https://support.apple.com/en-us/HT211094
This relaxes the set points around re-charging (based on your usage patterns) and can improve long term battery lifetimes. When active, recharging may stop short of 100 percent charged.
I have it connected to the AC power into one of the USB C ports. The battery indicator shows that it is charging - but for some reason it occasionally decides to stop charging and the system drains the battery.
Your computer performs best when connected to AC power. It can use the full output of the Power Adapter AND when doing especially challenging work will also freely "borrow" power from the battery. In some cases, the charged state may even decline during stressful work.
USB Power Delivery sources such as your power adapter or displays only send power after a successful negotiation with the computer. No Power source can "force itself" on your Mac -- your Mac chooses from all available.
Your computer may connect to the first seen major power source. Some say it will connect to the "best" source, but we don't have enough reports from Users to confirm or deny that.
Grant Bennet-Alder wrote:
Your computer may connect to the first seen major power source. Some say it will connect to the "best" source, but we don't have enough reports from Users to confirm or deny that.
Included in the ‘some’ that say that is Apple. “If you do plug in more than one AC adapter, your Mac will automatically select the single best-suited power source and charge from it.”
Charging while monitors plugged in
