If i was to make a battery pack with 4 18650 batts (2 in series and 2 in parrellel) total voltage is 7.4v With the two leads coming from this can I make contact with my terminals on my 18650 battery charger as if I was charging one 18650?? and charge the batts this way.......help needed
Charging in serial parallel is a bad idea. I know from first hand with NiMH batteries it does not charge evenly. I would not dare try it with Li-ion. Others will have more info, but it's not recommended from what I read.
No, unless you're using a hobby charger your standard LiIon charger would not be of high enough voltage to charge the 2S2P config. The EYE30's battery carrier is exactly in this config but the built-in charger is capable of charging up to 8.4V in either 2S1P or 2S2P config. Take a look at the charging graph in my EYE30 review as I tracked each individual cell's starting/ending v but keep in mind, these are relatively new cells and reasonably well matched - albeit I haven't done any internal resistance testing
Would your pack be sealed preventing you from easy disassembly? These cells will likely come out of balance sooner or later so you'll need some way to get them balanced again.
Cheers,
Tim
+1 on both
you need a hobby charger, or you need to make it easy to remove cells from pack and measure carefully before reinserting
I had some really great advice, but not for your question. 
Oh, well. Maybe next question.
But I had this Maha NiMH charger that would only work if 2 cells were inserted. It pretty much ruined all my NiMH's over time. Now I have a new charger and new cells and charge those only 1 at a time.
I'm a little out of my depth, but the guys that sell this: http://www.batteryspace.com/pcbfor74vli-ionbatterypack8alimitwithfuelguagesocket.aspx might have something for 2s2p. (A really quick survey showed that a lot of their pcbs had big minimum orders, though, so that's a drag.)
Thats for all the info. I think I will be creating a battery pack that I can charge the cells separately. With creating a 2p2s set up will I get double the run time than just 2 18650 creating 7.4v.
You can change the parallel banks without separating batteries, because charging two x mAh Li-Ion's in parallel is exactly same as charging one x*2 mAh Li-Ion (thanks to them charging by voltage, not by dV / dT detection like NiMH)
is not the same you need to balance the cells, take care
or buy an hobby charger/li-ion balance charger and/or the right pcb
or as cheapest and easiest solution buy 2 of this and charge the cells separately, better if that are protected and of the same brand/age/(effective)capacity
+1
I've tried charging cells in a parallel holder (w/o my balancing hobby charger). it didn't work, and I have no idea why they didn't just balance on their own. Probably because I was trying to apply a super low trickle charge to revive scavenged cells (so they varied greatly in capacity). It was probably pretty dumb and dangerous...
It IS same, balancing only applies to cells that are put in series, not in parallel.
As long as you parallel cells with equal SOC, everything should be fine. Of course, paralleling a fully charged cell with a empty one would be a dumb thing to do.
I mean balance the cells first of charge or put them in parallel, for that I added or to the next solutions
you can consider also the lifepo4