> A smart charger can detect if a battery is present, or at least some load that is safe to dump power into.
> defaults to 5V 2A charging
i don't think you understand how power transfer works.
voltage is applied (by the charger), and current is drawn (by the device that wants to charge). a charger cannot "dump power into" anything.
when chargers and devices attached to them engage in some sort of negotiation, that's not the device telling the charger what to do, that's the charger telling the device what its limitations are.
if you attempt to draw 3A from a device that can only do 2A, the voltage will drop outside of the specified range. to the extent that a charger can limit the charging current, it does so by dropping/cutting off the voltage until the current goes down. which isn't ideal for devices.
(perhaps you're confused by thinking that USB "chargers" are like battery chargers, and arbitrary USB devices somehow act like batteries. that's all wildly wrong.)
I'm aware. The potential "dumps" current into the load proportional to its voltage. (A constant current supply would raise the voltage to achieve the requested current but the USB bus is not a constant current supply. There are multiple ways your yes-but is annoying and unhelpful.)
The main concern behind negotiation seems to be safety of the user and safety of the power supply. Detecting a safe load means detecting a not-short.
The basis for the 5V power negotiation on USB is extremely silly. The power supply is already current limited, protecting you from shorts, and the supply voltage is ~5V, quite far from anything dangerous.
> The basis for the 5V power negotiation on USB is extremely silly.
This may be true for wall chargers but not devices capable of supplying power to peripherals while on battery power themselves.
For example, an external hard drive should not have to figure out that a large tablet can power it, while a phone won't, though trial and error, by attempting to spin up the disks multiple times.
True, but opt-in seems to do what users expect most of the time. Enough device expose their full power without negotiation that there are workarounds like sleeping a USB port instead of relying on power negotiation.
Devices are going to misbehave anyway, it's probably more important to default to a reasonable level of mostly works.
> defaults to 5V 2A charging
i don't think you understand how power transfer works.
voltage is applied (by the charger), and current is drawn (by the device that wants to charge). a charger cannot "dump power into" anything.
when chargers and devices attached to them engage in some sort of negotiation, that's not the device telling the charger what to do, that's the charger telling the device what its limitations are.
if you attempt to draw 3A from a device that can only do 2A, the voltage will drop outside of the specified range. to the extent that a charger can limit the charging current, it does so by dropping/cutting off the voltage until the current goes down. which isn't ideal for devices.
(perhaps you're confused by thinking that USB "chargers" are like battery chargers, and arbitrary USB devices somehow act like batteries. that's all wildly wrong.)