This is an update to this post: Sometimes Things Cost More Than Their Price
To sum up, I was trying to decide whether to get rechargeable batteries for our baby swing or return the swing and get one that plugs into the wall - either option seemed to make a lot more sense than buying disposable batteries on the regular (Baby M loves her swing!). I opted to get the rechargeables.
Just before I ordered them, though, I stumbled upon a whole bunch of reviews saying that the batteries don't work very well, don't hold a charge for long enough, etc - and these people had specifically purchased the batteries to run baby swings, so I was paying close attention to their concerns. Peanut explained the reasoning to me - something to do with the number of volts in a disposable versus a rechargeable battery.
And then he came up with the perfect solution: he hacked the baby swing using and old cell phone charger, so we now have a swing that plugs into the wall for half the price of the fancy one! He assured me that the whole thing was very safe and it certainly works perfectly. And the best part - we had the old cell phone charger just lying around, so this hack was totally free! Aside, I guess, from the miniscule increase in our electricity bill.
SO: Peanut to the rescue. I will never again complain about all the little bits of electronics he collects, because no doubt he will be able to rig up something else in the future. The takeaway is to find a better solution to any problem - and then find an even better one than that!