Changing cell count

[Ejay]

I have recently bought several 2s and 3s zippy 5000mah lithium batteries. How hard would it be to change 2 3s batteries and 1 2s battery to 2 4s battery's, I am thinking that maybe keeping everything 4s or 2s x 2s makes sense.
Thanks
Ej

[NativePaul]

How confident are you at soldering? Do you have a decent iron with a big heavy tip? Do you have steady hands and good eyes? Do you have big brass balls?

You need the confidence and equipment to be able to unsolder and resolder very quickly as the tabs are aluminium which heats up very quickly and are only a few mm away from the cells so it would be easy to overheat them inside the cells degrading them or worse. As soon as the solder has liquefied you want to remove the heat and immediately pry the tabs apart before the solder solidifies again, if you can fit an insulator under the tab to pry with things are less risky but there is not always room and I have blown the tip off a scalpel blade prying with it before, either way I would suggest wearing safety goggles as there will always be a chance of slipping with the iron or overbending a tab onto another tab and shorting some cells resulting airborne molten metal droplets.

[Make-a-Wake]

Its semi-risky/tedious but I have made four 3s out of three 4s. They MUST be the same mah and C rating to match them together.