Believe it or not there is still stuff out there that needs batteries to operate. Proper AA batteries, not unremoveable rechargeable batteries that break down after a few years. A lot of them (toys included) get gifted at Christmas, and you can easily get caught out. Thankfully Black Friday and Cyber Monday mean you don't have to.
Duracell batteries are discounted over on Amazon today, with a nice 40% discount on lots of different packs. Including 18-packs of AA and AAA batteries, which are worth noting because they're the most common batteries you'll have to use.
Because what sadist designs a product to work with C batteries? Or something that needs 9V batteries that isn't some sort of science kit for kids? Of course if you really do need some of the, you can go hunting for deals yourself and get yourself stocked up.
The AA and AAA packs are both £9 each (down from £15.29) and means you're basically paying 50p per battery. Which is pretty good, assuming you haven't been cheaping out on Poundland batteries all these years.