I recently purchased two Anker PowerCore 20100 (Nintendo Switch edition) battery banks that use the USB-C Power Delivery (PD) standard. I am using these with an Apple Macbook Pro, and they work well to provide up to 24 W of extra power, greatly extending the life of the onboard battery.
However, I was hoping it would also be possible to charge the PowerCore batteries from the computer when it is on an AC adapter. But this doesn’t happen. This means that if I deplete both Anker batteries and my onboard battery during the day, I need to plug each of them into my single recharger in succession to recharge for the next day, which requires a lot of attention at the right times (possibly in the middle of the night). Or I need to buy two more USB-C chargers for the extra batteries in order to plug everything in once overnight. I would much rather plug the two PowerCore batteries into the laptop, plug the laptop into the wall, and leave all of them to charge overnight.
As I understand it, when the PowerCore is plugged into the laptop, the laptop negotiates to find the highest output the PowerCore can produce. If there is no other power supply plugged into the computer, it will tell the PowerCore to switch to that mode, and then draw power from it as needed. However, if the laptop is already on its own power adapter ( > 24 W), then it will continue to use that, and tell the PowerCore not to deliver power. And that’s the end of it – nothing more happens (i.e., the PowerCore does not start charging from the laptop).
Would it be possible to update the PowerCore firmware so that if the PowerCore is plugged in but the laptop doesn’t draw power from it, the PowerCore switches over to charging itself from the laptop instead? I’m not sure if this is allowed by the Power Delivery standard, but it would be really handy! Or maybe you could add a Mac driver that achieves this, if it can’t be done from the PowerCore side? Alternatively, if there were some button sequence to force the battery into recharge mode (press and hold the side button until it starts charging?), that would work well too.