Recently (and unbeknownst to me for over a week) my son bought my daughter a new battery for her car. Lacking the tools to do an immediate install, he placed the battery on her back seat. He (and she) forgot about it for several days and upon remembering, found the battery had leaked acid all over her back seat. She has been driving now a couple weeks with this acid in the cloth seats and on several occasions, forgetting it is there, has placed several items of clothing on top of the spot only to find holes in them later. How can I neatralize this? Or will I need to find a new back seat?
The acid can be neutralized by appling a mixture of baking soda and water and then vacuumed up with a wet/dry vac. But you’re still going to need a new rear seat.
Tester
And do that more than once.
Then do it again next week.
But it’ll never stop eating. Slowly , lika a cancer it will keep eroding the facric and padding.
Agree; I once replaced a battery wearing old jeans that were still good. Small droplets of acid must have landed on the pants, since they gradually disitegrated.
Yes, you need a new backseat, which should be readily available from a wrecking yard. “Fixing” is just not cost-effective.
The baking soda and water solution will neutralize the acid attack and stop the damage from progressing…Some fabrics will tolerate acid better than others…If the seat is ruined, it’s ruined…
You’ll want to remove the seat and make sure the acid didn’t drip down to the floor of the car and eat that as well. Battery acid is sulfuric acid. It’s eating anything it got onto RIGHT NOW. It doesn’t take long to do a lot of damage.
DO NOT WAIT TO LOOK INTO THIS.
Check it and put the baking soda solution on it NOW. Keep putting the solution on it until it stops foaming.
It May Not Hurt The Seat’s Fabric Or The Padding, Depending On What Their Composition Is. Don’t Forget That The Acid Doesn’t Eat Through The Battery.
Others are correct that the seat should be removed and cleaned and any acid underneath should be neutralized, too. Those springs will corrode.
Some fabrics and padding can be 100% synthetic (as in “plastic”). I regularly filled batteries when I worked at a dealership and one time flooded some acid all over my pants. I was mainly concerned with getting the acid off my skin and washed my legs off immediately.
Surprisingly, the acid never damaged the dark blue pants nor caused any discoloration. They were made of some type of synthetic fabric (no cotton, wool, etcetera). For all I know they were made from recycled milk bottles or recycled battery cases. 
Time will tell.
CSA
I’d remove the back seat. That’s easy to do on most cars. Then I’d douse the back seat and the area under the back seat with a lot of water in order to dilute any acid that might otherwise be overlooked. Get rid of as much of the water as possible, then douse the seat and any carpeting that might have been dripped on with a lot of Sodium Bicarbonate dissolved in water. If it doesn’t fizz, the acid is probably defeated. Douse the seat/carpet with water again. Wipe up the water and dry the seat for a couple of days in the sun. When you can no longer find damp on the seat/carpet, put everything back together and pray.
Unfortunately, all that should have been done as soon as the spill was discovered rather than now.
If the seat falls apart, you will need to replace it. Maybe a salvage yard can come up with a reasonable color match.
To remove a back seat, run the front seat all the way forward, get in the rear area and push the lower seat edge rearward and lift at the same time. The seat will pop up and you can then lift it out…