Xiaomi protocol: https://electro.club/m/29042 (Google Translate. For Xiaomi scooter but protocol are said to be similar)
Someone built an Arduino firmware to connect any battery to a Xiaomi scooter (Google Translate and find the right post): https://electro.club/m/188889
Unpacking a random sample of packs
We unpack 30 random packs from Step to measure the voltage of the cells and determine the % of good cells in these batteries
Procedure
Unscrew all 4 screws on top
Pry the top plastic case with pliers
Pry open the half plastic case to access the cells
Measure each group of 2P cells and write voltage in the table
Diagnose, add verdict
Close pack and add sticker (Perfect, OK, KO, others)
Take photos/video of the process, time it
“Good cell” criteria
All cells < 2.0V are discarded (we could test cells > 1.8V but not without EIS)
Unbalanced when differences > 0.2~0.3 V
Verdict choices
PERFECT: all cells perfectly in balance, with voltage > ~3.0V
OK: all cells seem OK. Some can be unbalanced
KO: all cells are < 2.0V
Others: one half of the cells dead, other half can be OK or unbalanced
Observations
We don’t see any relationship between tapes on the packs and the health of the cells
Most of the time bottom half of the cells are more discharged than top half. Probably because the BMS takes its supply on lower half of the cell stack (5S)
However, sometimes it’s the top half that is lower, which is strange
Step 30 packs analysis
Pack
Cell voltages
Observations
Verdict
Score
1
All 3.65~3.67
Red tape “BLAD 45” Red blink seen once
PERFECT
1
2
2.67 2.8 2.87 2.72 2.9 / 0.3~0.37
Red tape
1/2 unbalanced 1/2 KO
0.5
3
2.55 2.78 2.51 2.89 2.90 3.35~3.35
Red tape
1/2 unbalanced 1/2 OK
1
4
0.9 0.9 1 0.9 1 0.9 1.15 0.9 1 0.9
Yellow tape. Red blink
KO
0
5
1.4 1.4 1.4 1.5 1.4 1.94 1.95 1.83 1.95 1.90
1/2 KO 1/2 KO?
0
6
3.40 3.40 3.40 3.40 1 1 1 1 0.6
Why high cells dead?
1/2 OK 1/2 KO
0.5
7
2 2.4 2 1.75 2.4 3.1 3.1 3.1 3.2 3.1
1/2 unbalanced 1/2 OK
1
8
3.6~3.6
PERFECT
1
9
3.4~3.4 1.2 1.2 1.3 1.2 1.4
1/2 OK 1/2 KO
0.5
10
2.7 2.9 3.0 2.5 2.8 0.9 0.9 0.8 0.9 0.9
1/2 unbalanced 1/2 KO
0.5
11
2.6 2.6 2.6 2.7 2.7 3.3 3.3 3.3 3.3 3.3
OK
1
12
2.7 2.7 2.9 2.9 2.8 3.4 3.3 3.3 3.3 3.3
OK
1
13
2.9 2.7 2.8 2.9 3.0 3.4 3.4 3.4 3.4 3.4
OK
1
14
3.1 3.1 3.1 3.1 2.9 3.4 3.4 3.4 3.4 3.4
Blue blink
OK
1
15
1.5 1.4 1.6 1.5 1.7 2.1 2.0 1.9 1.9 2.3
1/2 KO 1/2 KO?
0
16
2.3 2.4 2.4 2.3 2.3 3.3 3.2 3.2 3.3 3.3
OK
1
17
1.7 1.7 1.8 2.0 2.0 3.0 3.0 3.0 3.0 3.1
Red tape
1/2 OK 1/2 KO
0.5
18
3.4 3.4 3.4 3.4 3.4 3.8 3.7 3.8 3.9 3.7
Yellow tape
OK
1
19
3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6
PERFECT
1
20
3.9 3.9 3.9 3.9 3.9 0.0 0.3 0.3 0.4 0.3
1/2 OK 1/2 KO
0.5
21
0.6 0.9 0.7 0.7 0.7 0.0 0.0 0.0 0.0 0.0
KO
0
22
0.9 0.8 1.0 1.0 0.7 0.7 0.6 0.5 0.5 0.5
“BRAK KADOWANA”
KO
0
23
1.6 1.5 1.5 1.7 1.7 2.7 2.7 2.7 2.7 2.8
Red tape
1/2 KO 1/2 KO?
0
24
1.8 1.4 2.0 1.9 2.0 2.5 2.4 2.4 2.2 2.7
1/2 unbalanced 1/2 KO
0.5
25
1.8 2.5 1.9 1.8 1.8 0.0 0.0 0.0 0.0 0.2
KO
0
26
2.9 2.7 2.8 2.8 2.9 3.4 3.4 3.4 3.4 3.4
OK
1
27
1.4 1.4 1.3 1.4 1.4 3.0 3.1 3.0 3.0 3.0
1/2 OK 1/2 KO
0.5
28
1.8 1.9 1.9 1.9 1.9 2.9 2.8 2.7 2.7 2.8
1/2 OK 1/2 KO
0.5
29
2.7 3.0 3.0 3.0 2.9 3.4 3.4 3.4 3.4 3.4
Solder on B4
1/2 unbalanced 1/2 OK
1
30
4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0
PERFECT
1
Good cell percentage
18.5 packs out of 30 with cells which should be good ⇒ 62% “good” cells
This excludes isolated > 2.0V cells when every other cell around it is < 2.0V, because is may not be worth it to go further with this pack
Cell cost calculation
2nd Life calculations sheet has been refined, especially to include a “good cell percentage”, in order to study the impact on 2nd Life tested cell cost:
