I have mentioned in these pages that I am the happy owner of a Google nexus 7 2013 tablet and that I was having battery issues. In May of last year I bit the bullet and bought a new battery, opened the tablet and replaced it. I thought I was out tof the woods but unfortunately one of the reasons the battery had gone off was the charging port being broken... Nearly impossible to find and VERY expensive. So repair was put on hold until just before christmas when I read an article that explained the cheapest way to recover use of the tablet was a Qi wireless charger. Last week I received the envelope from China and lo and behold the 3.99 € (including postage!) plastic disk worked its magic!
The point of this introduction is that the battery in tablets and phones has a PCB that is a kind of BMS not unlike those in bike batteries. Even though it is a single cell in most cases it needs to be controlled for max voltage and min voltage for example. This PCB also give information like mAh and temperature, important in the use of LiPo in a device permitting automatic switching off if the temperature goes beyond a certain limit. In the system software there is a history of the battery usage as well which calculates how much time the device will run on remaining charge.
Having swapped out a worn battery for a brand new one has left me with a silly problem: the tablet switches off saying that it only has 4% battery left even though there are still 3.7 Volts left. I thought it was going to be easy to reset the system statistics to zero and start afresh but alas no... I charged up to 4.2 V and ran the tablet down to "zero", or rather its idea of zero, several times to no avail. The only solution I have found was to gain root access and install a calibration application which is running as I type these lines.
The messy details are:
- 3.8V LiPo single pouch cell which cuts off at 3.528 V and charges to 4.3 V max (I reached 4.291 V last full charge)
- 3950 mAh capacity
- 15 Wh
Back in the day those 15 Wh gave me about 10 hours use (web, video, music, games...)
The point of this introduction is that the battery in tablets and phones has a PCB that is a kind of BMS not unlike those in bike batteries. Even though it is a single cell in most cases it needs to be controlled for max voltage and min voltage for example. This PCB also give information like mAh and temperature, important in the use of LiPo in a device permitting automatic switching off if the temperature goes beyond a certain limit. In the system software there is a history of the battery usage as well which calculates how much time the device will run on remaining charge.
Having swapped out a worn battery for a brand new one has left me with a silly problem: the tablet switches off saying that it only has 4% battery left even though there are still 3.7 Volts left. I thought it was going to be easy to reset the system statistics to zero and start afresh but alas no... I charged up to 4.2 V and ran the tablet down to "zero", or rather its idea of zero, several times to no avail. The only solution I have found was to gain root access and install a calibration application which is running as I type these lines.
The messy details are:
- 3.8V LiPo single pouch cell which cuts off at 3.528 V and charges to 4.3 V max (I reached 4.291 V last full charge)
- 3950 mAh capacity
- 15 Wh
Back in the day those 15 Wh gave me about 10 hours use (web, video, music, games...)
