OK, so I watched the above posted video and I have a couple questions that pertain to that circuit and how I could make a circuit for my situation.
What I have is a standard 12 V charger that can charge at up to 10 amps, however, I usually keep it around 4.5 amps when charging. The battery pack is a pack of 4 lithium ion cells that are each usually resting around 3.3 V charged. My goal is to have them start discharging at 3.5 V when being charged.
I drew up a circuit that is similar to the one in the above video but accounts for the 4th cell in the pack.
http://i.imgur.com/mBp8lfs.jpg (Circuit diagram)
Does that circuit look correct? The charge controller is going to be the 12 V charger, and the discharge control is going to be handled by light bulbs.
What I want to do is have the Arduino monitor the voltages off the individual cells and have code that will send a HIGH signal to the corresponding MOSFET if it detects a voltage higher than 3.5V. The MOSFET will have a 5V gate voltage that will activate it from the Arduino's HIGH signal. Acting as a switch, the MOSFET will allow the bulb to turn on and act as a drain on the specific cell.
So, I'm wondering if this can be accomplished with the circuit diagram pictured above and just what that would look like.
http://i.imgur.com/N98KOmB.jpg(Sketch of what the arduino could look like in connection with the batteries)
What would the circuit diagram for this look like? What kind of light bulbs, resistors, and MOSFETS will I need? How can I protect the Arduino from the higher current that the Lithium Ion cells will give off? I'm pretty confused as to how to approach this, so any help is greatly appreciated. If I'm not providing sufficient information, please let me know and I'll do my best to provide more information.
http://i.imgur.com/5PGsYJe.jpg (The charger)
http://i.imgur.com/gSiPv4b.jpg (The battery pack)
http://i.imgur.com/n8HFEDh.jpg (The component for the balance plug)