Battery Charging Problems [Q2686RD - R7.46 ]


Hi guys,

I am experiencing some problems regarding battery charging. I hope you could bring up a solution.
The problem is that the battery charging is not performing well.

Environment Configuration:
AirPrime Model: Q2686RD
Firmware: R7.46.0.201108091301.Q2686RD 2216044 080911 13:01
Battery Config (LI-Ion).
The device is always connected to a charger.

First Test:

We left the device plugged to a charger for 12h, the next day it was uncharged.
I don't have any log about what happened. I guess that the first charge was well, after that it started to decrease voltage and it didn't recharge again.

Battery Config:
	1) AT+WBCM=4,1
	2) AT+WBCM=3,1,4200,3400,4700,1438,601,1,2000,0

Second Test:

Again, we left the device turned on during the night, this time we got the logs. 

The first charge started (+WBCI: 2, <voltage>), when the voltage reaches the maximum (around 4300mV) It started to decrease the voltage (+WBCI:2, <voltage>).

Until It reached a voltage of 4050mV, then It showed the +WBCI: 1. (WBCI: 3, <voltage>) the software tried to launch the recharge process (AT+WBCM=1),but the device continued to lose voltage (+WBCI: 2, <voltage>).

After that we tried to execute directly some AT commands. AT+WBCM=0 and AT+WBCM=1 to try to reset and to start the charge again. The +WBCI's are OK, but the battery didn't get charged.

Battery Config:
	1) AT+WBCM=4,1
	2) AT+WBCM=3,1,4200,3400,4700,1438,601,1,2000,0

Third Test:

This time, we have turned off the Automatic Charge Resume. The only difference is that we didn't get the +WBCI: 1. 

Battery Config:
	1) AT+WBCM=4,1
	2) AT+WBCM=3,1,4200,3400,4700,1438,601,0,2000,0

I have been running tests all the week and this bad performance appeared yesterday, the rest of the time it worked well.

Does anybody have any idea?

Thanks in Advance.
Iago Tejeda


Hi everybody,

we are still doing some tests over the battery. I’d like to show you the graphic with the battery levels.

We recharge the battery by code (WBCM=1) when the voltage is aroround 4050mV.




Just a thought - how good is your charging power supply?

If I recall correctly, the docs indicate that the charging supply must be current limited as appropriate for your battery as the Q2686 only modulates the battery terminal voltage.

If the charging supply sags when a load is put on it, it’s going to confuse the Q2686 charging algorithm. Stick a oscilloscope on the charging supply and the battery terminal voltage and see what happens when the Q2686 charging is running.

Also, does your battery have the protection circuitry built in? Maybe you are tripping something there?

ciao, Dave


Hi Dave,

first of all thanks for your reply. I have has to send these information to the person in charge. And he has told me that …

  1. The charging supply is limited to less than 800mA as the manual says.

  2. We are already using built in charge-circuit in other projects with Q2686H modems, and no error has been reported.
    If the built in charge-circuit were wrong, it would fail in all tests. wouldn’t it?

We have tried to resolve this problem by shutting down the modem’s charge algorithm.
Instead we are monitoring the charge values (+WBCI: _), and we start/stop the charging supply when the modem reaches a min/max threshold.