Sooner or later you'll need to cut the cord...the power cord! Untether your electronic project from the tyranny of the wall adapter and take it out into the world. That's where batteries come in, and you may have been seduced by the high power density, large current capabilites and recharge-ability of Lithium Polymer or Lithium Ion batteries. These battery chemistries have quickly become the most popular rechargeable batteries in consumer products, powering everything from keychain mp3 players to huge laptops.
Thanks to the big market demand, the price of lipoly (for short) batteries has plummeted. Now you can get batteries for $10 each, or even 'recycle' batteries from old cell phones.

However, these batteries need a special type of charger! You can't just use a NiMH or NiCad battery charger, even a LiFePo charger wont cut it. Instead, a proper Lithium charger is required.
Adafruit has a few small basic chargers that can satisfy your LiPo charging needs. All of these chargers can only do 1-cell chargers for 3.7V/4.2V cells. These are by far the most common and all the LiIon/LiPo batteries in the Adafruit shop will work quite nicely.

Battery Types

Check your battery before plugging it in!
The Mini/Micro Lipo chargers all are for 3.7V/4.2V cells only. These are single LiPoly/LiIon batteries. Some very old types of LiIon cells are '3.6V/4.1V' type - not good! Also, dont use this charger on Lithium coin cells, there are rechargeable coin cells but they are best used with a custom charger.
This is a Lithium Ion battery, often cylindrial with a tough metal casing. It clearly shows the voltage (3.7V) and capacity (2200mAh)
This is an example of a Lithium Polymer battery. They look like silvery pouches. This one is a 3.7V 110mAh battery.

Plugging In

You can plug in either the battery first or the USB port first. We provide a JST jack since the large number of batteries we carry come with a JST PH connector or cable
If you are soldering on a JST cable or using a non-Adafruit battery check the polarity of the wires going into the battery port. A backwards battery can destroy the charger!

USB Port

USB ports are very handy around the house, you can use any USB port that is on a motherboard. If you are using 500mA charge rate, try to avoid using extension cords! Even for 100mA charge rates, we suggest not plugging into unpowered hubs (most hubs are un-powered), keyboard ports, monitor ports, etc.

You can use USB wall adapters such as those for tablets, phones, GPS, MP3 players, too!

Charge Indictator LEDs

There are two LEDs on each MicroLipo charger.
  • Red - this means the chip has detected a cell and is charging it
  • Green - this means the chip has completed the charge cycle and the battery is ready to go
  • Both - this means the battery is damaged or isn't plugged in.

Charging other batteries

We strongly encourage using Adafruit batteries for your projects since they are new, come with protection circuitry and have the right polarity JST cables.

There may be situations where you need to charge a random battery and you can't solder a JST cable to it! In this case, you can usually hack something together.

For example, here's a GoPro battery that discharged all the way and couldn't be 'revived' by the camera.
You can see its a 3.7V 1000mAh battery. That means we can charge it at 500mA max rate if we wish.

On the back, though, there are these clippy connectors!
By soldering two pins of male header onto the JST cable, we can set up a delicate-but-workable charging cable!

Charge Rate

When charging Lithium batteries, its important to keep track of the charge rate. A rule of thumb is, you should max charge at 1C of current. For a 500mAh battery, thats 500mA. For a 2200mAh battery it's 2200mA. Pretty easy!
This rating is just the MAX rating, you can always charge at a lower rate - it just takes longer.

You can estimate how long it takes to charge a battery by taking the capacity, dividing by the rate, and multiplying by 125%.

For example: a 2200mAh battery charging at 500mA? It'll take 2200/500 * 125% = 5.5 Hours. Less if its not fully drained!

Changing the Rate

The chip in the MicroLipo can charge at up to 500mA rate. To make it safe for all our batteries, we set the default rate to 100mA. It's very easy to update the charge rate, however. On each board, look for the solder jumper that looks like this:

Melt some solder onto the jumper to close it and set the new charge rate

Constant-Current / Constant-Voltage

There's a few stages for charging batteries: pre-conditioning, constant-current and then constant-voltage.

Pre-conditioning is when the battery is very low, and requires low current. Constant-voltage is for 'topping up' the battery when its almost completely full. Constant-current is where the bulk of the charging occurs. If your battery is not ready for constant-current or if it is coming out of the CC stage, it will draw less than the max charge rate current!



All three Micro-Lipo's use essentially the same schematic - but with different USB ports

Fabrication Prints

This guide was first published on May 30, 2014. It was last updated on May 30, 2014.