I have a in dash dvd player and an overhead 15" flipdown monitor that are linked to the battery

then I have a x box 360 plugged into a 800 watt inverter to the battery.....before the 360 I had a gamecube.......I have no idea what the draw is on each accessory but I was playing a game and my inverter turned off twice within a 6 hour period. It doesn't sound like the 360 because I would think that the 360 would cut out first and the inverter would still be on......

Someone help me

upgrade batter/ possibly get better alternator/switch wire gauge??

One other thing im not sure if its amps or ohms but the display reads out between 12.9 to 13.4 when the 360 is on then off

 

the xbox 360 sucks alot of power... no, the 360 won't turn off before the inverter..

if the invertor sees that the 360 is sucking too much power.. (or more actually that the battery is dying because of it)... it'll turn off... which is what it's doing.

even an upgraded battery will have a hard time keeping up powering up that 360... even with the engine on and the alternator running!

that massive game console draws about 160 Watts!!

 

A very long extension cord?? Seriously invertors are not very efficient to begin with and running a high draw item like the 360 off it is going to drain the battery. The best solution for longer play without low volt shutdown would be a larger capacity or second battery to increase the power pool. A higher amp alternator would help recharge either single or dual battery setup faster. You didn't say if you were running the engine while you are running the 360, doing so should help as well.
Seems to me some inventive sort should make a power supply (mostly a voltage divider to supply 12V and less regulated power to the units parts) to run it on 12v without the inversion step ( I am assuming maybe wrongly that the xbox is like most computers and runs 12V d/c or less throughout the device)...then you could just plug it in to a car or boat and it would go alot longer for the same amount of available D/C power (no inversion loss)

 

How about one of those stereo capacitors that’s used for high drain amps? I could be wrong but maybe if you put one of those between the battery and the inverter it would solve your problem. just a suggestion