What happened to my battery ?

 I've heard of campsite shore power being wrong and damaging converters, but never at home. Have you had the Pod plugged into 120VAC while having lighting storms?

The loss of electrolyte in a flooded lead acid battery occurs through gassing as hydrogen escapes during charging and discharging. You will also lose water when a battery that is run at elevated temperatures thru evaporation. In California my battery sits in a black box exposed to the sun and can get warmer than the ambient air temperature. I check my battery before every trip and need to add water about every 3 months. I also keep the trailer plugged into AC power when it’s parked in my driveway so the battery is always charged up.

If your plates were exposed, that battery is damaged--that capacity will never be fully regained.  But you can refill it with distilled water (only!) and use to diagnose the charger before a potentially bad charger ruins a new set.  Voltage should be just under 15 but more important the amperage needs to drop as the battery nears full charge.  Monitor for overheating.  If it's still pumping in 30 amps after 24 hours and the voltage hasn't dropped, the charger is suspect.  Ideally let it charge for 36-48 hours, the voltage should have dropped to a float voltage just below 14V.  Unplug it and let it rest for 2-4 hours and check the specific gravity of the cells to get the state of charge and check the battery voltage around 12.65V is 100% but it could be higher due to surface charge if u don't wait.  If unable to do all this, just pop the caps after two days of "trickle" charging.  If they're still actively bubbling it's not a trickle!

I had the stock converter/charger in our 2013 '177 suddenly cook a set of group 24's that I had just checked levels on maybe 2 weeks before.  Nothing like pulling out steaming batteries and watching them boil for an hour on the driveway.  Threw it all out and moved up to a pair of GC2's and new converter/charger.

You should not be encountering new batteries with missing electrolyte in the consumer-grade market.  Check levels when u buy a battery. If it's low, someone spilled it, really old stock, or a manufacturing error.

Now that we have more info I will address this from a different vantage point.  I purchase a fair amount of batteries at the business I work for (golf course).  Local vendors sell their batteries with electrolyte in them.  If they are shipped from a distance, they come dry because UPS or similar will not transport them wet.  So possibly you got a dry battery from the start or the battery was sold with a low amount of electrolyte in it?  I have seen this happen every now and then.  Check the POS where you purchased your battery from; they may come dry and you have to add the electrolyte yourself.  Let me know if that is a possibility.  If not, there are electrical gurus on this forum who can walk you thru the process to check the potential overcharging question.

You probably need to get a new charger.  As the above poster noted, "you were getting more than a trickle",  I would second that with 100% certainty.  With your water level way low, you were overcharging and the electrolyte evaporated.  Monitor next charge with a voltmeter as was mentioned.  I am quite convinced your battery is toast, will have to purchase another.

My 2 deep cycle 12V group size 24 batteries were purchased March 2011.  Every winter when our pod is in hibernation mode they sit on concrete from November to April.  The first year they sat in our basement, after that in our unheated garage in northern Michigan.  They receive a trickle charge (2 amps) in November when we finish camping, it usually takes a good day or a tad more for each to reach 100%.  The following March I will give them their 2nd trickle charge before taking them out it April.  Again it takes 24 - 36 hours to bring them up to 100% SOC.  Still work well, 5.5 years old, check electrolyte a few times per year but will only add distilled water to them maybe once/year if that. 
The misnomer of no batteries on concrete goes back to the early days when battery cases were constructed of wood, and they would lose their charge sitting on concrete.  All batteries that I know of today are plastic cased, so that is no longer an issue.