Arrowmax have introduced 5mm to 4mm reducer sleeves for LiPo batteries. Different with most other similar products on the market, their use is very simple: just insert into the 5mm plug on the LiPo to effectively converting it to 4mm. No need soldering, the reducer sleeves are very convenient to move from pack to pack. You can maintain your charging cable and ESC connection with the same 4mm plugs and still being able to use LiPo with 5mm conncetion. They come as pairs and are 24K gold plated for maximum conductivity.

See: Arrowmax