These are <i>way</i> more expensive than I expected. Prices between 50–80 USD for what amounts to a wall-wart tethered to a battery-shaped piece of plastic with metal contacts.<p>Amazon has similar products in the 10–20 USD range. Still a lot of money, but far more reasonable.
Neat idea. Just tonight I went to use my dr ho and realized I left it on last time killing my battery. Almost thought about hooking it up to my variable power supply.