Change all batteries at the same time, don't mix battery brands?

For real or battery company propaganda? The reason I ask is because I had to replace some batteries in a clock that takes three double-As and I only had two spares, of a different brand. The package tells me I am doing a Very Bad Thing, but I replaced two of the three batteries. The clock runs just fine so I’m thinking this is a scuzzy attempt by the evil battery consortiums to build enforced brand “loyalty” and over-consumption. Who’s with me?

Well, you’re both right. It’s not a good thing to mix used and new batteries, because the good batteries can push too much current though the older batteries, causing overheating and possibly leakage. However, in low-power devices like clocks and remote contrtols, this isn’t the issue the instructions make it out to be. Mixing battery brands isn’t gennerally too bad, but imbalances in various factors, such as internal resistance can cause problems in some equipment. Again, not the end of the Earth. Generally, don’t do it if you can avoid it, but if you gotta it’s not going to blow up.

I’ve noticed in one of my remotes, that if I do this, the old battery will reverse polarity! (And it doesn’t even destroy the bad guy.) It’s weird testing a battery and having the pos end be neg.

Note that a remote is a very low power device.

Well, as a theoretical matter, in a low drain device, you will get a longer life from a set of fresh batteries if they have the same discharge characteristics - i.e. they are from the same maker, and are in an identical state of charge.

As a practical matter, if you use comparable brands (e.g. don’t mix top quality alkalines with El Cheapo Mundo “ship 'em with the product to keep the customer happy that first day” batteries) then the difference will be much smaller. After all, there’s always some variation between indvidual batteries. I suppose it would stand to reason that you would theoretically get the absolutely best performance by only using batteries from the same package (identical storage conditions, and probably, batch numbers)

As an even more practical matter, it comes down to what you do with the batteries you remove. If you save them and sort them by residual voltage for re-use in a less demanding device, you’d probably get more total life out of every 100 batteries than you’d get by chucking them and starting with a fresh set. Of course, that’s a hassle, which is an expense in terms of your time and storage – and remotes tend to leave such a low residual voltage by the time they conk out that you’d probably be wasting your time.

Sometimes one cell goes dead well before the others. In taht case -assuming you don’t keep trying to use the divice, you may save a few cells with appreciable life left in them.

I did stuff like that as a grade school electronics geek. As a teen, I checked final voltages out of curiosity, and saved the better ones for the inevitable times when a family member bummed a battery off me (Sometimes it seemed like I was the only one who regularly bought tthem, and I hoped to make bumming my hard-bought batteries less of a convenient solution) Today, I buy batteries in bulk, for less than my friends spend on piecemeal replacement, and since a single buy lasts me for years, I live the carefree profligate life of a ‘battery millionaire’ (Throws batteries in the air “Triple-As for ev-ry-one!”)