Ah, well if you can figure out a way to wire them in, you may be able to get a fully charged laptop battery to do this. But I don't think there are any off-the shelf items for what you want to do. Factories in China are always making stuff though, check some of the trade sites. I don't recall exactly what it's called, but there is a international trading site setup like eBay where people can order OEM parts from factories.