Dead Battery...DOH!

[N231BN]

It doesn't boil off the water. The chemical reaction produces an excess of hydrogen. The battery has a safety vent to release the hydrogen if the pressure gets to high. When you over charge it you lose some hydrogen. When the charge state tries to get back in balance there isn't enough hydrogen and it sucks the sides in. Water isn't what it is lacking, it is hydrogen.
That's why they are called recombinant gas batteries.
http://www.tms.org/pubs/journals/JOM/0101/Nelson-0101.html
 

Sorry for being a little loose with the terminology. The net result is the same however. In an overcharged condition electrolysis occurs and once that happens you are never getting that water back into the electrolyte.

The difference in a sealed Concorde vs a Gill is electrolysis always occurs when a Gill is charged, hence the need to add water.

[laytonl]

I have completely drained my Concorde AGM twice because of the cabin lights.  Each time the battery came back up okay after three days on a battery tender.  Battery is still working fine after 6 years.  After the second issue, I changed the lamps to LEDs and had Don Muncy send me a schematic of his timer but I have not built one yet.  He has a simple circuit which I believe used a darlington pair for the time delay.   Should work great.  Lee

[DonMuncy]

8 minutes ago, laytonl said:

I have completely drained my Concorde AGM twice because of the cabin lights.  Each time the battery came back up okay after three days on a battery tender.  Battery is still working fine after 6 years.  After the second issue, I changed the lamps to LEDs and had Don Muncy send me a schematic of his timer but I have not built one yet.  He has a simple circuit which I believe used a darlington pair for the time delay.   Should work great.  Lee

Lee, Before you build the timer, check back with me. At one time, my circuit diagram had an error, which I have now corrected. 

And don't dawdle around. If you have got by with running a battery down twice without ruining it, you are already pushing your luck  

[laytonl]

Don, I sent you a PM.  Lee