greeting to all
on Sunday i have converted the 4 s 2400mah 35 c li po battery to 3s
as local engineering students  bought 2 4s pack for their hovercraft project and esc with the capacity of 3s only they have no time to buy new one as their demo is on Wednesday. so i decided to convert that battery pack to 3s did lot of research then finally take risk of converting
bellow is the images.
and battery are in good condition and working well.
after soldering just repacked with packing tape with some thick double side gum tape for protection from damage  .
"i know the risk associated with and before start i taken lot of precautionary measures " 

you are great. u can choose Tattu 3s battery, i use it, it's good.