LiPo Power Source for GPS-GSM-ACCELEROMETER-433 REMOTE Control

Hello all , i am building a project for my bike ,

i am using GPS-GSM-ACCELEROMETER-433 REMOTE Control for it.

i was having some power problems with the GSM module when i was calling my phone ,

i start using a 3,3 Lipo , i had a nice 12v to 5v adaptor > a small lipo charger > and a 3,3V to 5v Converter Step Up Boost Module , And as i was thinking that this will do the job done.

I was thinking wrong ,i found with a meter that the GSM module gets 3,3wat when is calling for some seconds (lot of juice), so it was working with erratic behaviour

i found a nice 2s Lipo battery 7,4 volt 850mili , and the entire project working flawlessly , i get instant phone call , SMS , the GPS fix in seconds , the 433 Remote can work from 100meters...

My problem now is how can i charge this 2s battery ?? the is no dedicated 2s battery car charger , only for regular 3,3 , i have the equipment with the 1s

i may i ask again…
how can i charge 2s battery , the unit will be placed inside car , so i need a 2s lipo charger is there any solution>?