Li-ion /Li-ion super pack arduino based charging/ discharging

Ok, I understand that Li-ion / Li--poly tend to be dangerous. I have read 1000's of pages into the subject. I need more help in the part picking side than the actual charging algorithm. Li-ion / Li-poly packs are usually charged with a constant current till 4.2V then a constant voltage is applied while the current naturally reduces till about 0.05C then it is full. Some cells do the same with 4.1, and 4.3V depending on chemistry. Actually they are not that complicated if you really get to the knitty-gritty of it you apply 5V to a cell and monitor the terminal voltage and current and you'll see it rises for example to 4.2V (the actual voltage depends on exact chemistry) and then the current Will drop the problem is once the current drops to the full level the voltage Will start to rise again I.e. overcharging Will begin. And Li-ion Will draw current and regulate that on it's own too till over charging begins. But after 80% SOC you shouldn't feed more than 1C current or heat Will start being a problem . But there is more than one way to skin a cat. Li-chemistry cells can also be impulse charged. Take a 5V source preferably less than 5C and pulse the charge three seconds on 12 seconds off or more and then check the voltage when it reaches the regular full voltage after resting 12seconds it is full. Impulse charging like this has benefits so does impulse discharging. So does mixing up regular charge methods with impulse methods, because impulse methods tend to increase internal resistance. Ok enough of a novel. Need to find highly efficient mosfets to either switch on charging or discharging of individual cells. That can be switched from a mini 328p type board, like a nano. I need mosfets that can handle 20A currents at 5V as well as 4.2-3.3V while the switching voltage Will be 3.3V or lower from the nano. Any parts you folks can recommend ? Cheap would be great :-) terramir

if you already know your requirements simply go to digikey or mouser and use their part selection search to pick what works for your application.

Yeah thing is I dunno two things would it be more efficient to switch the positive or negative of the battery B. Do mosfets act like diodes and Will they block reverse current? I understand Li-ion but electronics I'm a little shakey on. And I dun wanna create a giant short circuit in the process. I want to design this in a way that it can charge cell A while cell B discharges, then let's say B while C etc. Most battery banks react pretty badly if you try to charge the cells while discharging. terramir