Convert Battery-powered Night Light to Rechargable

We have a 7 years old foster daughter who once or twice a week stays the night with us. She always wants a light on during the night, and from god knows where she got this (to me rather ugly) Paw Patrol Skye night light.

The problem is (or was) that these lights are running on 3 cell batteries that last only 1 or 2 nights. After going through a set of 20 of those batteries I found rather cheap on eBay, I decided to convert Skye to a USB-rechargable night light.

This instructable describes how this is done on this Skye light but you can use the same procedure for any other similar battery-powered light.

Materials:

• Battery: the old batteries give 4.5 volts so to keep the leds burning, a Ni-MH cell won't work so I need to have a Li-Ion cell that will fit in Skye. I found a cheap 160mAh battery on eBay.
• USB charge unit: for a few €/$ you can find aTP4056 board on eBay that does what's needed (being charge a Li-Ion battery from USB)
• 1 resistor 18kOhm

Tools needed:

• sharp knife
• small flat + philips screwdriver
• soldering iron

With a small flat screwdriver I could easily pry out the battery compartment with the switch and leds. It's a very simple circuit with a switch and a resistor in series to 2 leds. I decided to leave the circuit hanging during the job, and just cut off the old battery connections.

The width of the board is no problem, but the length is. With a sharp knife I cut an opening to let the board sink a little deeper.

With the the board in place it was easy to get the exact location for the USB hole, and using the sharp knife again this step was finished in no time.

The TP4056 board typically uses a charging current of 1 A. I assumed this is way too much for my tiny battery. Looking up the data sheet I found maximum charge is 80 mA. So we need to change the charging current if we don't want to set Skye on fire. After some research I found the charging current is controlled via a resistor on pin 2 of the 4056 chip.

The board has a resistor of 1200 Ohm installed which gives a charging current of 1A. The data sheet tells that the charging current is 1200 divided by the resistor value. Or, the required resistor value is 1200 divided by the wanted current (in my case 80mA or 0.08A). 1200/0.08 is 15000, so we need a 15kOhm resistor. To be on the safe side I opted for 18kOhm.

If you use another type of battery you can do your own calculation.

I didn't have any smb resistors lying around and I didn't want to suspend the conversion project, so I removed the 1200 Ohm smb and carefully soldered a normal 18k resistor in place. I know this may look a bit ugly but it does the job.

There are a few different versions of the TP4056 boards available so the location of the resistor may be different. Look up the data sheet (Google is your friend, and also Bing AI may help).

With a few tiny screws I secured the board in place to prevent it from shifting up when inserting the USB connector. As an alternative I suppose you can use hot glue.

Then the led circuit and the battery were soldered to the board. After a quick dry run (yeey everything works!) I squeezed the assembly back into Skye's pedestal.

When the USB charger is connected, the red led on the board shines up which is clearly visible through the plastic. This should change to blue when fully charged.