This charger is the only one you need to keep all your Lithium Polymer (LiPoly) or Lithium Ion (LiIon) rechargeable batteries topped up. No matter the power source at your disposal! The Adafruit Universal USB / DC / Solar Lithium Ion/Polymer Charger can use USB, DC or Solar power, with a wide 5-10V input voltage range! The charger chip is super smart, and will reduce the current draw if the input voltage starts to dip under 4.5V, making it a perfect near-MPPT solar charger that you can use with a wide range of panels.

Even though we designed it with solar in mind, it's also great as a plain USB or DC charger - we like that you can use 5V or 9V chargers without worry, and the high charge rate is great for quickly charging up those large battery packs!

Compared to our earlier, MCP73871-based charger this universal charger has some nice improvements:

USB Type C port for modern computers and chargers
Up to 1.5A charge rate
Up to 10V input voltage, 28V protected
Load output is regulated to never be over 4.4V so it's safe for 3.3V regulators or 5V boost converters
No stabilization capacitor needed (although you can add one if you like!)
Same load sharing so that DC/USB/Solar is prioritized over battery power when available, to keep the battery from cycling
Power Good LED lets you know that the charger is working
Less expensive

The bq24074 which powers this design is great for solar charging, and will automatically draw the most current possible from the panel in any light condition Even thought it isn't a 'true' MPPT (max power point tracker), it has near-identical performance without the additional cost of a buck-converter.

Features:

3.7V/4.2V Lithium Ion or Lithium Polymer battery charger
Charge with 5-10V DC, USB or 5-10V solar panel, can have both USB and DC plugged in at the same time, higher voltage source will be used.
Automatic charging current tracking for high efficiency use of any wattage solar panel
Use any 5-10V solar panel
Two color indicator LEDs - Power good and Charging
Set for 1000mA max charge rate, can be adjusted to 500mA or 1.5A by soldering closed a jumper
Will always draw the most current possible from a solar cell - up to the max charge rate!
Smart load sharing automatically uses the input power when available, to keep battery from constantly charging/discharging, up to 1.5A draw. Load output is regulated to no-more-than 4.4V