PMIC

The gamepad's power management IC is a Texas Instruments SN1010007. So far no datasheet has been found.

It is connected to the UIC's I2C bus, where its device ID is 0x48.

Pinout

Pin	Desc.
1	??
2	??
3	??
4	??
5	Battery pin 1 (red)
6	Battery pin 1 (red)
7	??
8	??
9	??
10	4.75V input from AC adapter
11	Battery pin 2 (gray) (through 510ohm resistor)
12	??
13	??
14	??
15	??
16	??
17	Ground
18	??
19	??
20	??
21	??
22	??
23	??
24	??
25	??
26	?? (to UIC pin 19)
27	UIC I2C - SDA
28	UIC I2C - SCL
29	??
30	Ground
31	??
32	??
33	??
34	??
35	??
36	??
37	??
38	??
39	??
40	?? (to UIC pin 17, with 100k pull-up resistor)
41	??
42	Ground
43	Battery pin 4 (white)
44	??
45	??
46	??
47	??
48	??

The gamepad is rated for 4.75V 1.6A. In practice, the PMIC accepts an input voltage of up to 5.2V (as often delivered by third-party AC adapters) without problem. This makes USB chargers a viable substitute for the proprietary AC adapter, as long as they can deliver enough current.

I2C communications

Communications to the PMIC always start by writing one byte, which is likely a register ID/address. Then further bytes are written or read in order to access the registers themselves.

The UIC firmware has code for accessing the following registers:

Register	Description
0x01	Charge status – bit6=AC, bit7=USB (1=connected)
0x02	??
0x03	??
0x04	??
0x06	??
0x07	??
0x08	?? – seemingly accessed after 0x07
0x09	Battery level LSB (format/bounds unknown)
0x0A	Battery level MSB
0x0D	??
0x0F	??
0x18	Backlight related – 0x90=on 0x10=off
0x19	Backlight related – maybe timeout/delay?

Which battery level is read out of registers 0x09/0x0A seems to depend on settings in register 0x07.