Battery in my truck went dead a couple of months ago. Tested it and determined I needed a new battery. Bought the battery, cleaned the terminals, and used special anti-corrosion pads and gel on the terminals when reinstalling. Truck started right back up with no issues. Drove it several times.

Parked it in the garage for a couple of weeks and just tried to start it. Dead battery. It's brand new. Jumped it, backed it out of the garage and shut it off. Went back out the next day and it's dead again. One terminal shows corrosion already.

Why would that be on a brand new battery? Any suggestions?

battery might be getting overcharged. I'd check the voltage with a meter while its running and see what the alternator is putting out

Gasses leaking from battery can cause corrosion. Undercharging can cause corrosion on one cable but not other; and overcharging can cause corrosion on one cable .

I've had good luck with giving the cable ends a baking soda bath, cleaning off the terminals, and applying some anti corrosion coating once reassembled. In a pinch I've used spray paint.

Might ditch the pads and coat with dielectric grease like Super Lube brand in the silver container. Have used this with success in a marine environment to repel corrosion.

Have had learned individuals over the years tell me not to use pads but don't know the reasoning behind it.

Also I'd put a digital load tester on that new battery just in case.

If it's overcharging, what's causing that? And what's the fix?

Probably a bad alternator / voltage regulator.

Might put a multi-meter on it and see what voltage you got at a stable RPM well above idle.

Is it a Ford?

Yes, 2008 F-150

It could be overcharging even if it's just sitting and not getting driven more than once every couple of weeks?

It's my old truck (just bought a new one), but I'm keeping it around as a spare and to haul our dogs in so they don't scratch up my new one.

You also might have a parasitic draw killing your battery.

Disconnect the ground wire and put the meter in between it and the battery terminal on amps and see what result.

Should be close to zero.

No help, but the reason I asked and maybe a rabbit trail to pick up...A video came across my YouTube feed the other day talking about this problem with Fords, and particularly so with a Ford/Motorcraft battery. I don't have a Ford, so didn't watch it.