This Adjustable LiPo Charger is a single-cell lithium polymer (LiPo) and lithium ion battery charger. Because it’s adjustable, this charger can safely charge Altus Metrum single-cell batteries with ease. With its onboard charge rate selector, you will be able to set the maximum amount of current to charge any battery from 15mA to 500mA.
The 100mA rate is the best choice for Altus Metrum 120mAh and 160mAh cells, the 400mA rate is ideal for 400mAh cells, and the 500mA rate is best for Altus Metrum 850mAh and larger cells.
Power comes from either a microUSB cable or the pins below the USB connector labeled GND and INPUT. You can easily use any cellphone USB charger, power bank or a laptop or desktop computer. Once power is connected, you can install a single LiPo battery to one of the three battery connectors, the JST connector, PTH pins marked BATT, or the 2450 coin cell holder on the back of the board. The input voltage for the charger is between 3.75V and 6V but to fully charge a LiPo battery, it is recommended to have a voltage of around 5V. The charger circuit will regulate the voltage down to safely charge the LiPo battery.
Note: The switches on the Adjustable LiPo Charger come shipped with all the switches in the ON position. Before configuring the board, all the switches should be moved to the OFF position.

Setting the Charge Rate
Regardless of the size of the battery, it's important to keep in mind the charge rate of the battery. Every time a battery is charged and discharged, it causes wear on the battery. The faster the battery is charged, the shorter the life of the battery.
Rechargeable lithium batteries have a maximum recommended charge and discharge rate measured in "C" (battery capacity). All of the single cell LiPo/Li-Ion batteries we currently sell have a maximum recommended charge/discharge rate of 1C (= one time the battery capacity). A 400mAh battery with a 1C charge rate would charge the battery at 400mA of current. The same 400mAh battery charged at 200mA of current would be 0.5C.
To set the charge rate, move the appropriate DIP switch from the off position to the ON position by sliding it to the right.

Setting a Custom Charge Rate
If you want to charge a battery smaller than 100mAh, or have a battery that's in between the values on the switch and would like to have exactly a 1C charge rate, you'll need to set a custom charge rate. This charge rate controller sets the maximum charge current with a resistor. To calculate the resistor needed, you can use the following formula:

[R_PTH (kΩ) = 1000V / I_set (mA)]

If you wanted to set the charge rate to 40mA for example, a 25kΩ resistor will need to be soldered into the unpopulated pins next to the micro-B USB connector. To use that charge rate, move all of the DIP switches to the OFF position and move the DIP switch labeled "PTH" to the ON position.

Battery Charging
Once the board is configured for the battery, you can connect power from either a micro USB cable or the pins below the USB connector labeled "GND" and "INPUT". To fully charge a LiPo battery, it is recommended to have a voltage of around 5V when connecting to those through hole pins. The charge IC will regulate the voltage down to safely charge the LiPo battery.
Once power is connected, you can then install a single LiPo battery to one of the three battery connectors on the board. If you're using the rechargeable coin cell battery, make sure the battery is installed in the correct orientation to avoid damaging the battery.
If using the coin cell battery holder, do NOT install any type of battery other than the rechargeable coin cell battery. Most other coin cell batteries are not rechargeable and will not work with this charger.
Once the battery is installed, the blue status LED should turn on. When the battery is fully charged the LED turns off.