I ask the question because it might jog others to do so. Or maybe I'm the only one dumb enough to not have checked mine since I've owned the car.

I have a 2013 Lexus RX 350. I only take it for maintenance every 10,000 miles instead of 5,000. And I go from Minor, Intermediate, Minor, Major Maintenance then vice versa. I have a little over 65,000 miles currently.

Last Thursday, engine wouldn't crank and I needed a jump from AAA to get home. Next morning, I figure I'd use AAA service where they come to where you are and install a new battery. Except the guy said he couldn't replace it himself and I had to first get the terminal connector on the wire replaced because it was all corroded.

It ended up costing me a whole lot more than just the battery obviously.

I generally look over the engine compartment when I'm waiting for the oil to completely drain.

The positive terminal has a snap plastic cover over it, and usually several other wires, fuses or fusible links connected to it as well. If this gets all corroded it can be frustrating and expensive to repair. Open that cover up every so often.

I remove and clean the terminals every six months as part of my PM schedule. Whether they look corroded or not, it can be there. A dark grey color is a layer of oxidation that can impede cranking.

When I have to replace the battery.

Bob

I treat the terminals with the purple spray, battery terminal protector, that keeps this from happening. Don't recall the brand. You can also use Vaseline or a thick wheel bearing grease to keep them from corroding. too.

If mine look corroded, I pour some Coke on them. I did not look at them on my previous car as the battery was under the back seat.

Often enough to keep corrosion from accumulating.

Every time I open the hood.

Which really isn't often enough cuz I don't put 5000 miles a year on the car so don't change the oil too often.

A bit more in the winter as I replenish the windshield washer fluid.

When ever I open the hood too.
Use this:
https://no.co/cb104

I remove and clean them every Fall.

If you aren't ready for Winter up here, you can lose body parts.

Once a month.

I check everytime I add windshield washer fluid about every month or two. ''

DEKA makes the BEST battery terminal protectant spray known to man, it's around $5 for a 12 ounce can and every DEKA battery dealer sells it.

Those little felt anti-corrosion rings that fit under the terminals work pretty well. Using those, I generally only check once a year or so, otherwise monthly.

Of course, this is on a 30-year-old car. Newer vehicles, not so regularly.

My wife has a RX350. Great car EXCEPT for the factory battery.
Three were replaced under warranty. One caused acid to leak a lot and that resulted in corrosion on the terminal. I checked the charging system myself after the first one thinking there had to be a (over)charging issue. There wasn't.
After the third one, I replace it with an Interstate I paid for myself and cleaned up the area around it well. That one has been working fine now for several years.

You can also spray "disk brake quiet" on the terminals to prevent corrosion if you don't have the dedicated stuff.

Every time I open the hood, which is usually every few months.

Pretty frequently, though not in a regular schedule. I open the hood pretty frequently between refilling washer fluid, replacing air filters, checking oil levels, and washing the car...

Just rolled 119k on my 2012 Subaru and zero car problems. I'm very aggressive with preventative maintenance and replacing wear items before they completely fail though.

Every couple of days when I'm jumpstarting my car.

I use a waterproof wheel bearing grease. Hit the posts after cleaning them, the inside of the terminals and then a light coat over everything once connected.