If you look at the link I posted, there are battery equivalents to the dynamo lights that I use and favor. The B&M Top Light Line (awful name) comes in a battery version, and is designed to go on the rack. It basically looks like a big reflector until you turn it on, and the light on top comes on.

*Edit -
Sorry - you may want blinking only, I missed that. But if you wanted to use a steady one, that's a good option.