The battery needs to be in place and hooked up for the 12V
systems to have power even when hooked to a shore power source. When hooked to shore power or a generator the converter (turns 110V into 12V
)provides power to the battery and keeps it charged as you "use up" the amps stored in the battery. With a digital volt meter check the voltage on the "new" battery. A fully charged 12V
battery should read close to 12.6 Volts. If the battery is fully charged and the shore power is plugged in it will read a 13-14 Volts. If those two things check out then look for blown fuses or a tripped 12V circuit breaker.