With a new baby, one of our life-savers that she loves is an electronic swing, which for some reason is battery powered.
I sure wish we could just plug it in, as we need to replace the batteries -- 4 D's -- about every 4 or 5 days.
Fortunately, we have a couple of battery chargers -- each several years old -- that work great, and several sets of rechargeable batteries. So instead of having to run out and buy new batteries every few days, and dispose of dead batteries every few days (into our electronics recycling bin of course), we just recharge 4 at a time and we're good to go. In this economy, if I had to buy each round of batteries we're using, I'd be crying as much as the baby!
I once read, I think in the Real Goods Solar Living Handbook, that a set of 4 rechargeable AA batteries lasts so many recharges that if you purchased those batteries one pack at a time, you'd be spending something like $1,600 (and that doesn't include the gas, time and parking from trips to the store).
I haven't been counting, but we rarely have to buy new sets of rechargeables -- so that sounds about right. As a bonus, of course, we're keeping hazardous waste out of the landfill, and reducing the amount of cardboard and plastic battery packaging that we have to recycle. Even better, rechargeables are wonderfully convenient -- plunking batteries back into the recharger for a few hours is much easier and less less time-consuming than having to go out to the store.
Using rechargeable batteries is really a no-brainer of a money-saving green practice. If you haven't gotten yourself a recharger yet, give it a try. You'll be glad you did.