K3 battery charge rate

[ilikepaper]

I am trying to repurpose my old K3 to a weather station display, using a raspberry pi 2.
Battery is dead, I recovered its PCB and used another Li-Ion cell so I can start the K3 and jailbreak/remove battery check, and everything is fine, but I would like to fully power it over USB, no battery.

Tinkering with it I noticed USB charge rate is at 500mA. I powered the Kindle with a bench supply (on battery connector), and noticed it seems to work fine with 4.5V and 1.5A limit, starts and works fine. I tried 1A and boot loops, so it seems to be needing at least 1.5A. I guess the battery would normally take these peaks.

So I've been thinking, I could route a single wire from USB port power pin, use a series diode and connect power directly on the battery connector Vin. That should drop 5V to 4.5V, and I figured if I'm using a 2A charger (with raspberry pi) then it should start.

But I could bypass the hardware mod if I could increase the USB charge rate, is it possible in software?

[ilikepaper]

In the end I just added a diode in series with the USB power pin, feeding it directly to the battery connector + terminal. And a 220uF cap after the diode, basically instead of the battery.
I had to use at least 5V/2A for USB wallwart, and a decent cable. Seems to work just fine without a battery. Added _SKIP_CHECK=1 in /etc/init.d/battcheck and dropped nobattcheck empty file in /mnt/us/system/ for good measure.

Raspberry Pi 2 cannot deliver the required current via USB, even with max_usb_current=1 using a 5V/3A power supply. So instead I used a powered USB hub, which I power with that 5V/2A wallwart, hub powers the Kindle, and it's connected to Raspberry Pi 2 via USB, seems to work great this way. Pi talks to Kindle via USB networking.