I’ve been trying to diagnose an excess current draw in my truck as it goes dead after just a few days of not being driven. In an attempt to troubleshoot it I took my battery off to put it in the charger when I noticed some corrosion in the underside of the hold down strap (see pics). I’m certain this wasn’t there before, any ideas what could cause this? It also looks like it has eaten away at some of the paint/powder coat as that was much better to my recollection as well.

I suppose it’s worth noting that I’ve got a group 65 battery in there so I’ve had to fabricate a little strap extension (not shown) to hold the factory hold down strap in place with the stock posts.

Spotted corrosion on the bottom before I removed it.

Flipped it over to find this.

 

You battery has caps on it and they're not 100% sealed and the vapors = cause corrosion

 

After reading up on some battery chemistry it would seem that this is Lead Sulfate which is caused by vapors released from the vent caps and they are reacting to the nearest iron thing (my battery strap) before they get a chance to defuse out. My strap probably has is an electrical ground to some degree and that’s why it’s reacting. I’ve been meaning to make a new strap anyway and am joust going to make sure it’s really coated well so there’s no grounding or iron to react with. Now on to actually tracking down that electrical draw...