How long does pancake batter last in the fridge?

Bisquick-originated pancake and waffle batter lasts a day, two at the most.

Data: in college, I made pancakes or waffles every day for a year and a half, making the batter on day 1 and then cooking it on days 1, 2, and 3. Once in that time I got sick on Day 3. Based on that experience, more than 24 hours is getting sketchy, though 48 seems to work most of the time.

Unless you're making flat "crepe" style pancakes, your batter will not really work properly later. Once the baking powder is mixed with wet ingredients, you need to cook it as soon as possible or its rising power will start to be lost. This will be true of any batter that has baking powder as its rising agent.

You're probably better off to make all your pancakes and then refrigerate the leftover pancakes. You can toast them to reheat them later.

I have no idea what type of pancake you're making, but I had answered your question for chemically leavened pancakes in case someone stumbled upon that question (even though the earlier question was specifically for crêpe like pancakes.)

If you're using baking soda as a leavening, it'll have already given its all by the time you cook it hours later ... but you'd have to add baking powder to compensate when it's time, as there might not be enough acid left for baking soda. Baking powder in the batter isn't as much of a problem if it's double-acting, where it'll give some leavening when it gets wet, and again as it gets warm. Of course, you don't want to add too much baking powder, as it can give a metallic taste.

It's also worth mentioning that it is possible to halve an egg; in this case, if you're going to be using the other half of the mix in a day or two, it might be easier to measure by mixing all of the wet ingredients together and then use half.

I found this site looking for the reason my premade pancake batter is turning out super flat pancakes. I have found without fail that the batter we make fresh everyday makes a fluffy pancake, without fail the next morning that same batter hits the grill and looks like a crepes .

Don't count on the batter lasting very long. Just make all the pancakes and freeze them. If you refrigerate them, they'll get pretty stale, pretty quickly.