What size and type of inverter are you using and what type of batteries do you now have? Are they wet cell or AGM? What do you intend to power with the inverter.
Also, you called it an 'inverter/charter". I assume that you mean it is an INVERTER/CHARGER. There is quite a bit of wiring required to get 12VDC battery power to the unit thru a class 'T' fuse and disconnect switch, and then having 120VAC of the proper wire gauge coming in to the unit with the same size going thru an appropriate auxiliary circuit breaker and then to your designated 'inverter outlets'. All must satisfy NEC requirements for a proper installation.
Tough to point you in the right direction without this information.