Sternwake:
When I build my next lithium pack it will probably be with GBS cells from the folks at the below link:
http://elitepowersolutions.com/
I like the extra safety that the Mn doping brings to the Lifepo4 chemistry. The four fastener cell interconnects are nice also.
If you look at the charge and discharge curves in the below link you will see that there is very little to be gained by charging above 3.45v per cell and discharging below 3.0v is pretty much a waste also. I have found that my 12v 40ah industrial Lifepo4 pack is in very good agreement with the GBS curves. The meat of the discharge curve is between 3.28v and 3.0v and is surprisingly flat. Matter of fact, one can charge my current pack to 3.45vpc, or any higher sane voltage above that, and within a few hours after ending the charge the cells will all be sitting at 3.28v plus or minus 0.01v. So why charge any higher than 3.45vpc? Especially since the consensus of the Lifepo4 cognoscenti is that charging over 3.45vpc is where the cell voltages really start to diverge. The number of charge/discharge cycles available should vastly increase also if the cells are kept in the 3.0-3.45v range.
Curves link:
http://elitepowersolutions.com/docs/Charging Discharging Curves.pdf
The below link is some good general info on Lifepo4 battery tech. The author seems to focus on top balancing but a lot of the more experienced folks in this field prefer to bottom balance. My research makes me tend to believe that the bottom balance route is a better idea.
http://www.pbase.com/mainecruising/lifepo4_on_boats&page=2
The link below goes into some detail of building an inexpensive BMS using Hobby King "data loggers", they are actually multi cell monitors that can be set to monitor for over voltage or under voltage with an output that can be used to control a LVD or turn off the charger if one or more cells go over the user defined high limit.
http://priuschat.com/threads/cell-logger-8s-help-with-operation-with-a-relay.123279/
Most commercial Lifepo4 BMS systems suck because of a lack of correct voltage set points with no adjustment possible or are far too expensive. The balance boards sold for the GBS cells turn on at 3.55vpc, lame.
The link below is the HK page for the voltage monitors.
http://www.hobbyking.com/hobbyking/store/__10952__Cell_Log_8M_Cell_Voltage_Monitor_2S_8S_Lipo.html
I did a long term test of ten months to see the self discharge of my 40ah pack. In ten months it lost 0.08v.
