I have a Q2686H, and the battery voltage reading is abot 300mV above what the battery really is.
Ussually, when the module starts the reading is ok for about 10s, then it suddenly jumps up. (Currently it is reading 4000mV when battery is 3700mV.) I am not running any Open AT apps. It makes no difference whether the battery charging interface is turned on or off, and also makes no difference whether I apply 5V to the battery charge input pins or not. The reading occasionally jumps back to the correct voltage after about 10 min, and stays correct for about 30s, then goes too high again. I am not using the ADC input. The AT+ADC? yields the same results as the unsolicited battery charge indications.
This is a problem for me as the battery level only gets to 3.9V before the Wismo stops charging it.