I have a cordless drill with rechargeable batteries. The batteries charge completely in about 20 minutes. They are not supposed to stay on the charger for longer than that. However, unless I am standing right there after the charging time, I forget to take the batteries off of the charger.
To fix this problem, I made a timed duplex power outlet out of a countdown timer and a duplex outlet. I plug the timed outlet into a 120v outlet. Then, plug the battery charger into the duplex outlet attached to the timer. Finally, I set the timer to 20 minutes and walk away. (There are more details about the parts and assembly on the Instructable.)
One problem I had is that the faceplate that came with the timer was too wide. It covered the timer and a bit of the duplex outlet. I found a Thing on Thingiverse that uses the Customizer to custom build faceplates that cover from one to five outlets with any configuration. I used it to make a custom faceplate for two outlets with a single hole for the timer on the left-hand side and holes for a duplex outlet on the right-hand side. I printed it on the Makerbot 3D printer using black PLA filament. I used 100% infill to make it solid and durable.
One problem I had with the print was that the raft stuck to the surface in some spots and would not come off. So, there are a few rough looking spots. Another problem is that the hole for the timer knob was a bit too small. I had to drill it out slightly bigger.
After attaching the new faceplate, I used my label maker to print the numbers for the dial.