How bad is it to mix old and new batteries?
“That’s like running a three-legged race with a less fit partner—not optimal,” says Alex Huang, Ph.D., professor and a chair of the department of electrical and computer engineering at the University of Texas at Austin. Say you have only one new battery for a two-AA remote that’s dying. Even if the remote starts up, the charge won’t last. The new battery has to work harder to make up for the spent one, shortening its life span. Meanwhile, the dud battery might overheat. Just get a fresh pair!
It’s ideal to use batteries from the same manufacturer; different brands’ voltage can vary slightly, and an electricity imbalance could affect performance. There you go, science lesson of the day.