DIY Rechargeable Battery Charger Upgrade for Safety

If you find that the batteries in your remote control are always running out quickly, it could be that you bought cheap batteries, so it's best to just buy rechargeable batteries. However, if the rechargeable batteries you bought get hot when charging, it might be worth opening them up to take a look:

Inside you'll find two diodes, four 6 ohm resistors, four LEDs, and a transformer - a typical circuit with no voltage regulation or timing, although it can be pulsed. It can be dangerous if you're not careful with charging times, so it can be modified to improve safety.

To modify it, you'll need:

1. A perforated board

2. An old phone charger

3. The components shown in the schematic diagram

First, let's take a look at the schematic diagram:

Here's the perforated board made according to the schematic diagram:

Next, here's the old phone charger which has been phased out:

Opening it up, we measured an output voltage of 5.04V that can provide a maximum current of 1.2A, and a voltage that is also 5.04V - it may have a wired connection.

We removed the USB port and it fit perfectly. We added a power indicator light for good measure.

The charging board was installed perfectly:

And finally, the case was closed and it's all set:

Additional notes:

The maximum charging current tested was around 120mA.

When the circuit is off, the battery voltage is 1.41V. We tested it with a multimeter and found that the battery is still charging even when the light is off, but it's a small current of around 40mA.