I have a situation I've not seen before. My TT has a plastic battery box with a deep cycle 12v battery in it. It is not a sealed battery. A few months ago when I went to get it out of storage (totally enclosed storage) there was a white powder on the concrete under the battery box and also on the frame where the box attaches. I opened the box and removed the battery and found a little liquid in the box (I had drilled holes in the box to drain any water that might get inside). There wasn't any of this white powder on the battery terminals. I figured that maybe I spilled some water when I filled the battery a month or so ago, or one of the cell covers leaked and while traveling and some of the battery acid sloshed out of the battery. Then the liquid drained out of the battery box onto the floor. I removed the box, cleaned it, cleaned the frame that the box attaches to, repainted the metal where the white powder had accumulated and reinstalled the battery. Everything was nice and dry and clean.Today I went back to check on everything, (the TT hasn't been used since I cleaned everything up) and the white powder on the concrete floor under the battery box and on the frame was back. There was no liquid inside the battery box and the inside of the box was clean and dry. The terminals on the battery were also clean.I do leave my TT plugged into shore power all the time to keep the battery charged and to operate a fan inside to circulate the air.I'm scratching my head and looking for help.Thank you.Pawpaw

The reaction between sulfuric acid and calcium carbonate* is somewhat similar to the reaction with sodium bicarbonate way - carbon dioxide bubbles out, and the salt is left behind is calcium sulfate.*Component of lime, limestone, cement, concrete

If you didn't neutralize the acid on the concrete that would be the reason the white powder appeared again.

Also, the PURPOSE of a Battery box is to CONTAIN any possible acid spill. To prevent acid from getting out and marring floors or rust the metal frame and box trays. If installed correctly with its lid(cover) water intrusion should not happen. If left plugged into 120 power, it is normal for lead acid batteries to sometimes boil and vent. The result is that white power. Doug

dougrainer wrote:Also, the PURPOSE of a Battery box is to CONTAIN any possible acid spill. To prevent acid from getting out and marring floors or rust the metal frame and box trays. If installed correctly with its lid(cover) water intrusion should not happen. If left plugged into 120 power, it is normal for lead acid batteries to sometimes boil and vent. The result is that white power. DougThanks! Looks like I messed up a perfectly good battery box by drilling a couple of holes in it so rain water would drain out if any got in. I'm going to patch the holes, clean everything up, repaint the metal frame and try again.Pawpaw

I always cover the vent holes on top of the battery box with small pieces of Eternal Bond tape. Regardless of the claims of the vent holes being needed to vent hydrogen gas from the battery box, there is plenty gap between the battery box lid and the battery box to allow hydrogen to vent away. Covering the vent holes will keep rainwater from accumulating in the Box.

white powder under battery box | Good Sam Community

MEXICOWANDERER
Explorer
Oct 28, 2017
The reaction between sulfuric acid and calcium carbonate* is somewhat similar to the reaction with sodium bicarbonate way - carbon dioxide bubbles out, and the salt is left behind is calcium sulfate.

*Component of lime, limestone, cement, concrete
Boon_Docker
Explorer III
Oct 28, 2017
If you didn't neutralize the acid on the concrete that would be the reason the white powder appeared again.
dougrainer
Nomad
Oct 28, 2017
Also, the PURPOSE of a Battery box is to CONTAIN any possible acid spill. To prevent acid from getting out and marring floors or rust the metal frame and box trays. If installed correctly with its lid(cover) water intrusion should not happen. If left plugged into 120 power, it is normal for lead acid batteries to sometimes boil and vent. The result is that white power. Doug
pawpaw47
Explorer
Oct 28, 2017
dougrainer wrote:
Also, the PURPOSE of a Battery box is to CONTAIN any possible acid spill. To prevent acid from getting out and marring floors or rust the metal frame and box trays. If installed correctly with its lid(cover) water intrusion should not happen. If left plugged into 120 power, it is normal for lead acid batteries to sometimes boil and vent. The result is that white power. Doug

Thanks! Looks like I messed up a perfectly good battery box by drilling a couple of holes in it so rain water would drain out if any got in. I'm going to patch the holes, clean everything up, repaint the metal frame and try again.
Pawpaw
mobeewan
Explorer
Oct 29, 2017
I always cover the vent holes on top of the battery box with small pieces of Eternal Bond tape. Regardless of the claims of the vent holes being needed to vent hydrogen gas from the battery box, there is plenty gap between the battery box lid and the battery box to allow hydrogen to vent away. Covering the vent holes will keep rainwater from accumulating in the Box.
BFL13
Explorer II
Oct 29, 2017
OP, you are not getting it!

First to clean up that white powder you need to use lots of baking soda (same stuff as used in a fridge) in some water to wash it away to counter-act the acid.

Next is why is this happening? Your battery is not in good shape and is leaking acid from one or more posts. Why is that?

Now it gets complicated. Can be a number of reasons. To get a start on that please state what converter you have and how you use it when not camping--eg--plugged in at home or what do you do if in storage somewhere, or is it left on solar between trips? What solar controller is that if so?
MEXICOWANDERER
Explorer
Oct 29, 2017
Antimony migration really aggravates a battery tendency toward increased electrolysis. So, if a voltage setpoint error cannot be found then a person should check the service date. The worst case I have yet seen was a set of US Batteries that would boil vigorously at 14.1 volts at 90F

Vigorously means rolling boil - caps removed, spitting electrolyte onto the lid.
2112
Explorer II
Oct 29, 2017
Did you check the water level in the battery again?
pawpaw47
Explorer
Oct 29, 2017
Thanks for all the advise guys.
The battery checked out OK at an auto parts store and water level was good. I took everything apart, wire brushed, rinsed with baking soda/water then plain water, repainted, plugged the holes in the battery box, and reinstalled. I also put a couple of those little donuts on the battery terminals. Then I plugged back into shore power. Now we wait.
I'll go check it in a week or two. Our next trip begins on 11/29. We're headed up to the Amarillo, TX area for a couple of weeks to visit Palo Duro Canyon and Caprock Canyon.
Happy camping!
Pawpaw
MEXICOWANDERER
Explorer
Oct 29, 2017
Might want to note that as compared to 70 degree water, baking soda in 180F water is manifold times faster acting and more potent a neutralizer. Works especially well for battery cable terminals. Oil saturated felt rings seal the lead post to plastic case junction. Use of rings is critical because even slopping on corrosion preventative is not really total protection without the felt rings.