Sorry for the delay with the promised complete writeup but I have a lot of work right now so I can't tell you when I'll be able to finish it.
Chast has already (for some reason) posted the CAN messages needed to run the scooter (and the battery) here, just in a completely unreadable format.
Here are the 29 CAN bus messages, cleaned up:
FORMAT: frame number, message id, number of bytes, message bytes
Code: Select all1 0x02181606 08 01 00 1E 01 01 00 02 00
2 0x03FF1601 08 6E 50 00 00 00 00 00 00
3 0x03FF1602 08 F2 43 27 00 00 00 00 00
4 0x02FF2602 08 98 40 EC DB 09 D1 69 0B
5 0x05124609 07 03 00 03 70 03 E8 00
6 0x05124609 07 03 00 01 B8 03 CA 00
7 0x02203606 08 01 01 00 01 00 01 00 00
8 0x04FF3400 08 00 00 00 00 00 00 00 00
9 0x05124500 02 01 02
10 0x02FF2602 08 EE F8 AA D3 2C 1C DF 1F
11 0x05124501 02 01 17
12 0x03FF1500 08 00 00 00 CE 00 00 00 00
13 0x03FF1501 08 00 00 00 0D 00 00 00 00
14 0x05124502 08 52 50 31 33 53 32 30 41
15 0x05124503 08 00 13 09 18 00 00 0D 6A
16 0x04FF3502 04 00 6F 00 66
17 0x05124504 01 13
18 0x03FF1502 08 01 00 00 00 00 00 00 00
19 0x03FF1503 08 01 00 00 00 00 00 00 00
20 0x03FF1504 08 00 00 00 13 00 00 00 00
21 0x05124611 08 00 64 25 FA 00 00 21 64
22 0x04FF3400 08 00 00 00 00 00 00 00 00
23 0x02FF2602 08 27 F0 D7 53 29 3E 33 5B
24 0x05124612 08 00 00 00 00 00 00 00 00
25 0x05124613 08 00 00 00 00 00 00 00 00
26 0x05124614 08 0F 94 05 0F 8C 0A 00 08
27 0x03FF1601 08 6E 50 00 00 00 00 00 00
28 0x03FF1602 08 00 00 05 00 00 00 00 00
29 0x03FF1400 08 00 00 00 00 00 00 00 00
For the people asking, the battery in ES400A is definitely communicating via CAN bus. I don't know yet which messages unlock the battery specifically, but you can simply send all of them, the rest will be ignored.
I managed to map out the battery connector (socket, looking down on the battery):

The pinout should be as follows:
1. +V
2. GND
3. Charger input
4. ?
5. ?
6. CAN_L (yellow wire)
7. CAN_H (green wire)
8. ?
9. Enable (blue wire)
When Enable is pulled low, the battery turns it's main voltage on and awaits messages.
That's all you should need to run the battery without a scooter connected, though I haven't had the time to test this out myself. Please reply if it worked for you.