What is a simple yet elegant way to read the voltage of all the cells?
This isn't an easy question. I've been working on this problem myself. The commercial solution is a PakTrakr. It's fairly expensive. The DIY solution is to use a microcontroller, scale the voltage of the cell down to the 0 to 5V range that most micros can read on their analog sensors, record that, and the graph the data using some kind of output device.
I'm not sure how far along you are, but here are some topics to look up:
- Voltage Divider or Voltage Dividing Resistors or Resistor Ladder
- ADC or Analog to Digital Converter
- Optical Isolation or Galvanic Isolation
I've got a little 4 cell monitor working on a lab bench. It was more of a challenge to connect up than I was expecting. What kind of micro controller are you using? I've been tinkering with Arduinos (ATMega 168 chips). They have 6 ADC channels so I could, in theory, use 1 micro to read 6 cells.
Here's an example of the data I was able to read off my my lab bench. This is 4 LiFePO4 cells connected to make a 12V battery. I ran a hi-beam headlight off of it for ~45 minutes until one of the cells in the series string hit low-voltage for the chemistry and I stopped collecting data to re-charge the cells.