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Reported full charge capacity many times higher than design capacity of Li-ion battery using gas gauge Bq20z95

Rasmus Larsson
Prodigy 20 points
Other Parts Discussed in Thread: BQEVSW

My company have a portable product with Lithium-ion batteries using the Bq20z95 gas gauge. Recently we have received back malfunctioning batteries from customers. The reported problem have been batteries which stop working when they indicate a charge of about 70-90%. Upon closer look, using the BqEVSW software and the EV2300 adapter, that the "full charge capacity" is many times, 3-4 times, the design capacity. We think that the gas gauge might be incorrectly calculating the capacity because it should not be able to become that much higher than the design capacity. 

I would appreciate any ideas to why the capacity might be reported to be so high. The design capacity is 8250mAh and the full charge capacity have been reported to be anywhere from 37444mAh to 60000mAh on different batteries.

  • 0
    TI__Guru 57697 points

    Hello Rasmus,

    This can happen if current calibration is incorrect on the pack. Specifically the current reads a charge current when actual current is 0.

    This causes charge current to appear higher and discharge current lower, so with a few cycles the capacity accumulates to show higher.

    If there are not enough rests, then the gauge does not get an opportunity to correct based on voltage.

  • 0 in reply to Shirish
    Prodigy 20 points

    Hi Shirish,

    Thank you for your reply. Ok, so the calibration has somehow turned incorrect. I see that in the bqESW-software there is an option to calibration the current. If I do a recalibration would that reset the calculated capacity value as well? 

    Also I didn't quite understand why the calibration have turned incorrect. What do you mean by "rests"?

  • 0 in reply to Rasmus Larsson
    TI__Guru 57697 points

    Hello Rasmus,

    Calibrate it and then send the RESET command for gauge to recalculate capacity.

    Rest means that gauge has no charge or discharge for a long time.

  • 0 in reply to Shirish
    Prodigy 20 points

    Hi Shirish,

    I'll give it a try! Thanks.

    Maybe we can adjust our charging algorithm to allow for more rest. I'll review it.

    Another point: the batteries with this problem all seem to have been stored with very low charge <1% for a long time. Could that be a cause for the calibration to become incorrect?

  • 0 in reply to Rasmus Larsson
    TI__Guru 57697 points

    Calibration data is stored in flash memory, so unless exposure to high temperature or other abnormal factors were present, the calibration should be accurate even if the bq20z95 loses power. To check calibration on the battery, you can disconnect batteries and use a precision power supply to check if the reported voltage and current are correct, assuming that is an option.

  • 0 in reply to Shirish
    Prodigy 20 points

    Thank you Shirash, I will try this and report back.

  • 0 in reply to Shirish
    Prodigy 20 points

    Dear Shrish,

    We have now checked the current and voltage of 1 battery using an electrical load. The reported current and voltage from bq20z95 is in agreement with the electrical load. We tested both 50mA discharge current and 2500mA discharge current. We did not perform a calibration as we thought the current and voltage already seem correct. We then sent the command RESET. The remaining capacity changed slightly 51755mAh, but it is still well over the expected capacity of 8250mAh. Do you have any other ideas what could be the cause? 

  • 0 in reply to Rasmus Larsson
    TI__Guru 57697 points

    Hello Rasmus,

    Can you attach a GG.CSV file from this pack?

  • 0 in reply to Shirish
    Prodigy 20 points

    DataFlashExport.csv

    Fullscreen logfiles.txt Download 
    bq EVSW Version: 0.9.59 for bq20z95 v1.50	
Device:950,Ver:1.50
2023-05-15 09:50:43	
           
Design Capacity: 8250 mAH
Design Voltage: 10950 mV
Specification Info: 0031 hex
Manufacture Date: 10-mar-2020 
Serial number: 0000 
Manufacturer Name: SCIBASE 
Device Name: NS01 
Device Chemistry: SAMS 

Sample	Stamp	~Elapsed(s)	ManufAccess	RemCapAlarm	RemTimeAlarm	BattMode	@Rate(@)	@TimeFull	@TimeEmpty	@RateOK	Temperature	Voltage	Current	AvgCurr	MaxErr	RSOC	ASOC	RemCap	FullChgCap	RunTimeEmpty	AvgTimeEmpty	AvgTimeFull	ChgCurr	ChgVolt	BattStat	CycleCnt	CellV4	CellV3	CellV2	CellV1	FETStatus	SafetyAlert	SafetyStat	PFAlert	PFStat	OpStat	ChgStat
1	09:50:47	0	0000	700	10	6001	0	65535	65535	1	26.55	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
2	09:50:51	4	0000	700	10	6001	0	65535	65535	1	26.55	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
3	09:50:55	8	0000	700	10	6001	0	65535	65535	1	26.55	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
4	09:50:59	12	0000	700	10	6001	0	65535	65535	1	26.55	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
5	09:51:03	16	0000	700	10	6001	0	65535	65535	1	26.55	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3721	0006	0000	0000	0000	0000	8441	0200
6	09:51:07	20	0000	700	10	6001	0	65535	65535	1	26.55	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
7	09:51:11	24	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
8	09:51:15	28	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
9	09:51:19	32	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
10	09:51:23	36	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3721	0006	0000	0000	0000	0000	8441	0200
11	09:51:27	40	0000	700	10	6001	0	65535	65535	1	26.45	11160	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
12	09:51:31	44	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
13	09:51:35	48	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
14	09:51:39	52	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3721	0006	0000	0000	0000	0000	8441	0200
15	09:51:43	56	0000	700	10	6001	0	65535	65535	1	26.45	11162	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
16	09:51:47	60	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
17	09:51:51	64	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
18	09:51:55	68	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
19	09:51:59	72	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
20	09:52:03	76	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3722	0006	0000	0000	0000	0000	8441	0200
21	09:52:07	80	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3722	0006	0000	0000	0000	0000	8441	0200
22	09:52:11	84	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3722	0006	0000	0000	0000	0000	8441	0200
23	09:52:15	88	0000	700	10	6001	0	65535	65535	1	26.45	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3721	0006	0000	0000	0000	0000	8441	0200
24	09:52:19	92	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
25	09:52:23	96	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
26	09:52:27	100	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
27	09:52:31	104	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3721	0006	0000	0000	0000	0000	8441	0200
28	09:52:35	108	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3721	0006	0000	0000	0000	0000	8441	0200
29	09:52:39	112	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3722	0006	0000	0000	0000	0000	8441	0200
30	09:52:43	116	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3721	0006	0000	0000	0000	0000	8441	0200
31	09:52:47	120	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
32	09:52:51	124	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3722	0006	0000	0000	0000	0000	8441	0200
33	09:52:55	128	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3722	0006	0000	0000	0000	0000	8441	0200
34	09:52:59	132	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3721	0006	0000	0000	0000	0000	8441	0200
35	09:53:03	136	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
36	09:53:07	140	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200
37	09:53:11	144	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3718	3722	0006	0000	0000	0000	0000	8441	0200
38	09:53:16	149	0000	700	10	6001	0	65535	65535	1	26.35	11161	0	0	7	100	628	51754	51754	65535	65535	65535	3500	12600	02C0	42	0	3721	3719	3722	0006	0000	0000	0000	0000	8441	0200

  • 0 in reply to Shirish
    Prodigy 20 points

    See my reply for attached files. I could not manage to export it as .csv, it defaulted to .gg. The .gg-file could not be uploaded to this website so I changed the file ending to .csv. I hope it works. I also attached log files from approx 1 minute of idling (no charge or discharge) for the problematic pack.

  • 0 in reply to Rasmus Larsson
    TI__Guru 57697 points

    Hello Rasmus,

    The GG.CSV file has Update Status = 04

    Normal values are 6 or higher. Check the value of Update status in the golden image. It should be set to 0x02 (or 0x06).

    If you post the GG.CSV file taken right after the programming the golden image, it will help me understand what parameters changed during operation of the pack.