http://www.realgoods.com/renew/shop/product.cfm?dp=4100&sd=4102&ts=1051068
http://www.realgoods.com/renew/shop/product.cfm?dp=4100&sd=4102&ts=1051069
http://www.realgoods.com/renew/shop/product.cfm?dp=1000&sd=1006&ts=1050212

none of the three listed seem to do the job very quickly, but they should be enough to top up one set of batteries while you are using the other
plus it is pretty light weight