I just put an electric bilge pump from Bluewaterkayakworks.com in my NDK Explorer. Weighs about three pounds; has a lithium battery; magnetic switch on the first deck bungee.
Outstanding! As I almost always paddle solo, it's nice to be able to simply put my spray skirt on while doing my re-enter-and-roll, then turn the pump on when upright, with the skirt on. I can paddle and brace while it pumps out. Absolutely worth it. The kayak is already heavy; what's three more pounds? Could save your life. (I carry a manual as back-up, secured on the underside of the deck in a mini-cell sleeve attached with adhesive. I use the Harmony pump, as the float is a smooth cylinder running the length of the pump, making it much easier to secure in a sleeve like this).