We voted to put Jato's 12 year old battery in a museum, but instead they are going to send it into space to power the International Space Station for the next 20 years. 

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Thanks, that gave me a good.  Funny thing last week, i went out to the garage and noticed the dome lights on in my 2013 Explorer, for the 2nd time in a couple days.  Also noted that it didn't turn over quite a quickly as before so took it in to a local auto parts store.  Found out it had one bad cell, "replace it" they told me, so I was curious as to how old the battery was as I purchased it when it was 3 years old and 'thought" I had already once replaced it.  Found out it was the 'original' battery, a Motorcraft was installed 8/2012, so it also lived a pretty good life.

As far as the 12 year old Interstate that may 'end up in a museum' (purchased 04/2011) maintenance is key, never been taken below 12.2 volts before recharging and it has been used A LOT.   The sister battery to it (same make, size) died 2.5 years earlier and I figure it was because when I first purchased this 177, thought it was a 'cool' idea that the Dometic fridge could run on 12v power.  Found out that it did, for about 4-5 hours and then the fridge would begin to beep.  Took it in the above auto parts store, they told me to trickle charge it for at least a day, which I did.  I was a slow learner and tried the same scenario a week later and would you believe, got the same result!  Fortunately my brother was present and brought out the voltmeter and said, "Don't do that again, that will destroy your battery - battery read 8.1 volts after powering the fridge for just around 5 hours.  So after taking it down too low twice, am quite sure its life was terminally shortened by my stupidity.

We voted to put Jato's 12 year old battery in a museum, but instead they are going to send it into space to power the International Space Station for the next 20 years. 

That was a disappointment to me as well.  I had hoped to have at least one plug powered on the battery.  In a 180, the plug under the dinette could be easily repowered with an inverter under the seat, behind the power panel.  It would, of course be very limited in the power available.  A 300 watt inverter could pull the battery down to 50% in 1.5 hours. 

Attached is a handy SOC vs Voltage chart for flooded cells. 

+1 on GG post.  Pick up a multi-tester or voltmeter so you know what S.O.C. the battery has as the indicator is unreliable at best.  For maximum battery life don't take your 12v battery below 12.2 v before recharging.  Currently I have two 12v batteries that run independent of each other, usually boondock so they get used a lot.  I expect to get 6 days total out of both batteries when night temps are in the 40's and the furnace gets used a lot.  Also run the HW and stove during this time as well.  In the summer when no furnace is used, they will last significantly longer.  I do not utilize either solar or use of a generator.  Batteries used: 12 year old Interstate group size 24 deep cycle and a 2.5 year old Trojan T-1275 that gives 160AH. 

All the 110AC outlets require (1) Shore power, or (2) Installation of an inverter (which converts 12VDC to 110AC). Inverters are not common unless you have a relatively late model Rpod.

The outlets will work and GFI can be tested and reset when I'm on shore power. Fuses and breaker panel seem to be in working order. I have hooked the trailer up to the batteries and ran the fridge over night to make sure it wasn't my fridge drawing on the batteries and depleting them and I dont think I have a parasitic issue. 

Sorry for my lack of knowledge in this area but I'm looking for a suggestion on what to do next.  Anyone out there have any suggestions?