Carole, what you need is a balance board. There are numerous types available, and you need one that plugs into your charger that suits 2S. You plug your various batteries into the board, and that feeds the charger correctly. Here's a couple of examples to start your search.
http://www.brentfordrc.co.uk/Scripts...idcategory=215
http://www.flighttech.co.uk/eshop-pr...Balance-Boards
If you want friendly and reliable advice, talk to Charles Butterworth at Nitroflight Models - he usually sets me straight on what's what in LiPo stuff! Tell him Peter with the Bantam charger sent you...
http://www.nitroflight.com/
HTH
