Originally Posted by modelworks
If you connect the nook to a low power pc port you will only be able to run the charging for 45 minutes before the charger IC stops. To start it again you have to unplug and re-plug the USB cable. The charge current for a 500ma usb port is about 440ma.
Interesting about the "low power" port. But I haven't seen one yet. Nowadays, many USB2 ports provide up to 1000 mA without negotiation. Originally, the USB specification required that devices connect in a low-power mode (100 mA maximum) and communicate their current requirements to the host, which then permits the device to switch into high-power mode. But the USB Battery Charging Specification changed that. In recent years I've tested several PC mainboards, and an Xbox 360, all of them provide around 1000 mA on USB2 ports without negotiation.
But the Nook HD+ won't make use of that and limit itself to the 440 mA you mentioned. Why? Because it uses the two data lines (D+ and D-) of the USB connection to detect dedicated USB chargers. If the data lines are shorted, the Nook assumes it's connected to a dedicated USB charger and it will draw up to 2000 mA (about 1880 mA in my measurements). If the data lines aren't shorted, it'll limit to 440 mA no matter if the USB power source could provide more.
Originally Posted by modelworks
The device fast charges at 1.5A using the charger and charges at 4.208V to the battery.
From where do you get the 1.5 A? Your own dmesg output says "adj_fast_ichg_lim: 2036, 240, 2036", and as I said, mine charges with around 1.8 A.
Also, the line in the dmesg output that gives away the charging speed isn't "CHARGE STATE". It always reads "= 2 (FAST CHARGING)" when an external power source is connected.
The line "DCP detected" is the real confirmation (DCP = dedicated charging port), and apparently also "VBUS STATE".
"VBUS STATE = 1 (USB host)" means the data lines are NOT shorted => max. current intake is 440 mA
"VBUS STATE = 2 (Adapter port)" means the data lines ARE shorted => max current intake is ~2 A.
Furthermore, keep in mind that power from the external source is prioritized to first supply the system, and then the battery. That is, the battery is charged with the "leftovers". Therefore, if you connect the Nook to a source from which it'll only draw the mentioned 440 mA, and you're continuing to use the tablet, then it can happen that the battery won't be charged, or even will be discharged! If you perform some CPU/GPU intensive tasks on the tablet, its power consumption can easily exceed 440 mA, meaning the tablet will use the external source in combination with the battery to satisfy its hunger.
- Nooks will only fast charge on dedicated charging ports, which are recognized by having their data pins shorted. That's more or less standard nowadays for generic USB chargers (USB Battery Charging Specification). However, some chargers still don't meet this requirement, and Apple has their own incompatible standard, naturally.
- Don't use your tablet if you want to charge it from a low-power source (i.e. USB data connection on the Nook), because depending on the workload, the battery will be charged very slowly or will actually be discharged.