Not sure exactly what your are doing in the plane, but in sounds like using 2 packs of 3 cells to make a 6 cell pack.  Perhaps for balance or room.  I'm not sure about weight/wire in the plane part.  I assume a Y type joiner for the power side of the batteries.

Are you removing the batteries to charge and then parallel charging, or single charging? 

Are you trying to charge in the plane, or out, with a single charger as a 6 cell pack?

If you want to join the balance plugs to one, try this

http://www.ebay.com/itm/JST-XH-6S-TO-2x-3S-BALANCE-SERIES-Harness-ADAPTER-CHARGE-AS-6S-Lipo-battery-/272099458882?_trksid=p2385738.m2548.l4275

You could hard wire the two into a single pack by soldering up your own Y for power and balance, but again not sure what you want to do.  It seems easy enough to take them out, unplug the series, and charge them together on a parallel board.

Add more info about your connections if I totally missed the point.
 

Sorry for the confusion

I already have a wire harness for the series connection  that I have been using to make the (2) 3S packs work like a single 6s pack. The problem is the harness and the battery leads take up a lot of room in the airplane not to mention that 1/2 ounce of weight I could save eliminating the extra deans plugs and wire for the harness.

What I would like to do is hard wire the two 3S into one 6S battery. I can make the power connections work properly, my problem is I dont know how to make (2) 3S battery balance plugs into one 6S balance plug...or even if it can be done.

Thanks and sorry for the lack of info

A few alternatives after re-reading what you are doing.  It seems that there are two separate issues, weight and charging.   

A simple solution to charging is to use the packs as you are and then remove them from the plane for charging. Once removed, use the mentioned balance plug Y harness for charging, and charge them as one with both the power and balance harnesses.  The balance harness can be removed for flying. Mark pack 1 and pack 2 so that the power Y and balance Y join the packs the same. 

Or create hardwiring of those harnesses using the harnesses as "templates," for some weight savings. 

Or hard wire the power Y and use the balance y for charging only which saves weight.

Another easy solution for charging is to remove the power Y connection, back to two 3 cell packs and use a parallel board to charge and balance the packs at the same time.  Technically simple, but same weight as now.

The lightest is to totally rewire at the solder end and make a 6 cell pack as above.  Technically a bit more difficult, but saves weight and fiddling each time, once done.

Or wait for better ideas as others enter the discussion, which could be the best idea :)

Thanks all for the suggestions.

Fred I think I will take your idea and buy the balance adapter and hard wire the packs

Tim, sounds great.  As emphasized, make sure that the power lead and balance lead are correctly connected.  The risk you will run is connecting the balance lead each time, minimized if leads and batteries are clearly marked. 

Sorry, I know it is not exactly the topic that has been put to discussion but can I charge two packs in parallel with having the balance plugs put in parallel as well? Thing is, I have 10 batteries but only two chargers. It takes me nearly 5 hrs to charge them all with two chargers only and I am not willing to buy more chargers.

The question is therefore rather whether the balancing of two packs in parallel works.

Any ideas? Please don't tell me to buy another charger capable to handle 4 packs 

Thanks!

Christoph

Thank you Fred, that is a really helpful article.

Christoph

With some luck, we maybe be able to convince TP that there is a need for a 6S 25 C 2200 pack.

Speak with Kim Quinette at TP.

 I  did just today.

It might help if others ask, too.