title_body: Can I use two 2s lipo batteries to power my FPV DJI goggles? The FPV DJI goggles can take 7.4-17.6 Voltage. I am using a 2S 3000mAh LiPo battery. My plan is to buy another of the same liPo battery and attach it with a female to 2 male TX60 connector, making it a 4s lipo battery of 3000mAh(14.8 - 16.8V) .
  Do I need to consider anything else?
upvoted_answer: Connecting the batteries in series or parallel brings two new issues with it that you need to consider before you start using them and they are both related to batteries that are not on the same charge level.
  
  If you put two batteries of a different charge in parallel, the battery with the highest charge will charge the other one and very high currents can flow which can damage your batteries.
  If you put two batteries of a different charge in series they will both discharge at the same rate during use and the battery with the lowest charge will discharge a lot deeper potentially causing a lot of damage.
  
  So if you want to do this always take this into consideration:
  Parallel connection: Make sure the batteries are at the same charge level.
  Series connection: Make sure the batteries are at the same charge level AND of the same capacity.
  So if you want the higher capacity and don't necessary need the higher voltage (in this case you don't): parallel connection is better and safer than in series.