unit91

My 68 is the worst I've ever experienced with there always being white corrosion around the battery tray area. The battery is not being overcharged, the battery is well secured and the caps aren't leaking/loose, and the battery is filled to the proper level. I've installed battery mats below the battery and against the battery tray/fender, and I use a terminal spray that works on the terminals and cable ends, but I'm just trying to figure out why this corrosion keeps appearing. Any ideas? Of all the cars I've owned or driven since 1966, this one is the most perplexing and frustrating.

Boogie's_AutoRama

I'm thinking you've got a leaking battery.
More than likely it's the top cover that is bonded on to the bottom case.
That bond can be easily cracked if it's dropped or bumped real hard.

You don't necessarily need the liquid leaking out to cause the white crystals to form.
Just the gas evaporating out a crack will do it.

Would be great if you had a spare battery to swap out (without having to buy a new one) to test that theory out.

To clean out that area, I've had great results dissolving a cup or so of baking power in a 3 liter soda bottle of water and washing down the whole mess. Rinse thoroughly with fresh water and paint or under coat when it dries.
Be very careful not to get any baking soda into the battery. It will kill it.

bop11

The caps are vented, so they are leaking or the battery has a vent tube like motorcycles. If they were not vented, the battery would explode from built up hydrogen from the charging. In normal charge, some sulfuric acid fumes will escape. How do you know the battery is not being over charged? Mechanical regulators are not good at "Float Charge".
Mustang suppliers sell lots of right inner fender walls as do other suppliers for other cars. Battery tray rot has been around since they started putting batteries in cars.

groho

+1 on the baking soda and hot water. You must neutralize the acid before doing anything else. If you catch this early enough you won't have to replace your battery tray. . .and fender apron. There's one fix for this, gel cell battery.

tx65coupe

I also suggest washing with the method mentioned. All unsealed batteries vent gases and battery trays have always been a victim of this issue, some more than others.

bop11

There are also battery mats available for this problem. They soak and neutralize any acid that gets down there.

unit91

Thanks to all. Have washed area with baking soda mix. Checked battery for cracks, etc., and didn't find any. Got some battery mats and some terminal spray. Hope all this helps.