You can get a pretty good idea by just looking at the spec sheets of your GP27 battery.
This is TROJAN GP27 model 27TMX specs.
This shows the battery will produce 12VDC @ 25AMPS for 175 minutes or 2.9 hours. This will run the battery down to 0% charge however which you do not want to do so you actually will only get 1.5 HOURS at the 50% charge state.
Of course your 400WATT Inverter loaded down fully will draw around 32 AMPS plus some loses from your batteries so your time going to 50% charge will be some what less.
You will have to know what your power drain is going to be from your 400WATT Inverter.
Your best deal is to run a home test and see exactly how long one battery will last.
I would not go anywhere off the power grid unless I have at least two working batteries.
This will get you in the ball park thinking.
Two of the 6VDC GOLF CART Batteries will produce 12VDC @ 25AMPS load for around 447 minutes or 7.45 hours. That is alot more power than two of GP27 12VDC batteries will produce. Two of these 6VDC golf cart batteries will be a bunch less cost than two of the GP27 12VDC batteries...
If you run down your batteries to 50% charge state then you will need to run your generator connected directly to your trailer shore power cable for three hours the next morning using smart mode converter/charger to get them back up to at least 90% charge state if you want to do this all of this all over again the next day...
Roy Ken
