We just replaced our set of two 12 volt deep cycle flooded 80ah batteries with two size 24 AGMs of the same amp hour rating.
The discharge profile is interesting with AGMs and is much better for trailers with heavier draw devices like slide outs. This is because the voltage drop pattern is different with AGMs as the batteries discharge. Our usage over 3 days only caused a .2 volt drop from 12.8V at full charge. So we did not need to use our vehicle to boost the voltage and move the slideout back in. With the older cheap deep cycles it would have been necessary even if they were new.
With the change to AGMs we should now be able to off grid without recharging or hooking up the tow vehicle to boost the voltage to move the slideout for at least 5 days. Whereas the less expensive stock deep cycles that come with most travel trailers from the dealer discharge to a lower voltage much faster. So they require a quick recharge to attain the voltage necessary for devices like slideout systems even when they are new.
My advice to anyone buying a new trailer is to spend the extra on an AGM battery setup instead of just going with the option of installing the dealer's cheapest deep cycle setup. Bargain in a decent battery system or buy the trailer at discount without a battery setup and install a good one yourself!
Our trailer can only carry two size 24 batteries or a single size 27 so it is important to choose an option that does not overload the A frame of the trailer hitch.
We do have the option of changing over to lithium but that would also mean expensive changes to the electrical a/c to d/c converter system on the trailer. Or isolating the lithium system from the charging system on the trailer so that a the trailer could use lithium batteries as a backup.
One interesting change could be to build an off grid box with lithium batteries in it. Keep it in the back of our truck and switch over to the portable batteries only when the trailer batteries are discharged. This change would require a simple setup with a switch and plug next to the existing disconnect setup. Not rocket science like changing over the entire trailer's charging systems. With a setup like that it might be possible to off grid for two weeks without recharging. Or worse, carrying around a generator and driving other campers nuts, like in some of the off grid aluminum slums here in British Columbia.
It is certainly nice not having to worry about running out of power in the middle of the night. Then having the furnace not start up in the morning or the water pump not putting out enough water to flush the morning dump. Or worst of all being forced to wait in line at the outhouses because you forgot to fill a bucket the night before to flush the toilet.
BEEN THERE GOT THE T SHIRT with a slow running bathroom fan and a red face after causing the evacuation of our Winnie Drop, a situation that can put a hell of a damper on what was a great morning breakfast that my wife was making!