In most cases the RV never "Switches" to battery power.. The one exception I know of is those RV's with a Magnetek 6300 and possibly a few other Magnetek converters.. They actually do SWITCH to battery.
Most modern RV's the battery is ALWAYS there.. it is in parallel with the converter which is what powers the lights et-al on Shore power.... But it also charges the battery.
However there are a few thigns that can prevent it from happening.
First.. Many, I dare say MoST Rv's have a switch somewhere... In my cast the actuall "Switch" is remoted, but the control switch is on a panel just inside the door. on the side of the step well.. This is a common location.
Other locations include the master "Control and sensor" panel, and on motor homes the dash.. Mine is labeled USE/STORE (Press USE and listen for a CLUNK, more on that later) some are AUX (And optionally a MAIN switch next to it, this is on Motor homes only) May be labeled BATTERY or DIsconnect on Trailers.
The clunk.. When I pressed STORE I heard the CLUNK,, but pressing USE did not clunk.. (Dirty switch.. I cleaned it the no-cost way and it hasd worked well ever since) The Clunk is the actual switch (SOlenoid) by the way.
Second... On the battery control center (Where the clunk-er lives) per the manufacturer there are supposed to be a pair of circuit breakers.. PUSH (HARD!!) TO reset type in the bottom of the box.. Mine was done differently but if those breakers are tripped.
Some RV's it is a fuse.
Tribble shooting (yes I'm a Star Trek fan) best tool is an automotove test light
This device, which you can find at many auto departments and every auto parts store looks like an ice pick, the handle is clear or translucent plastic,, there is a light bulb in the handle, and a wire with a clip that comes out of the handle.
Clip clip to battery NEGATIVE, touch battery positive,, BRIGHT LIGHT = Good battery
(Do this when not plugged in)
Move clip to any unpainted metal part of chassis/frame.. Still bright light. Good,, No light,, Check battery negative cable and also clip connection point.
Now move out along the positive cable,, Find where the other end of it connects,, Make sure you get a bright light.. This will be a device with two or 4 terminals, if it is 4 pay attention only to the two big ones (the other two are control power) and touch the 2nd big one. Still bright, keep following the wire.
Each time you move the clip re-check the last good point to make sure you have a good ground.
Problem exists between BRIGHT and DARK.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times