i have had no problems with my game ceasing to work other than going zangief on the thing.
also, pokeymans, i decided to try out the pokewalker thinger. threw my cyndaquil in the thing, walked my walk of 3600 or so steps according to the thing. well, i then spent some of the "watts" which for every so many steps you take, you get one watt, from my 3600 or so steps, i got about 150 watts. you can catch pokermans or get items, i really only picked the catch pokemon option, and there was doduo and pidgey, so i caught both. i would assume you get different pokemon depending on the "route" you take, since when you connect the walker with the ds, you can choose a set of places to walk in, i chose the first option, but there was only two to choose from. seems like you can unlock new routes when you get more watts, so walk more, get more paths. also there is a gift option which i did, i don't know what i got yet since i haven't gone into my game per say, just the main menu to access the pokewalker stuff. the two really cool things in my opinion, the pokemon you catch in the walker, they go to your pc box, so they are actual pokemon you can use in the game. the second, cyndaquil leveled up from said walk, yeah, he leveled up.
the short version of this
-pokewalker is kind of cool, it like earning stuff for the game as you are out and about doing whatever
-you catch pokemon in it which you can use in the game
-your pokemon can level up in the thing
-you can get items with it
i haven't tried the linking pokewalkers to eachother, but when i do (i bought my game with a friend of mine, so i have silver, he gold) i will report on it.
all in all, it's a pretty neat little device. as for battery, i don't know how long it lasts, but it goes into a "sleep" mode when not touched for 20 or so seconds, in this mode it can still sense steps you take and whatnot. but due to this, i can assume you won't need to change the batteries for a long time.
*edit*
http://bulbapedia.bulbagarden.net/wiki/Pokewalker