Introduction: Power Stacker: Stackable USB Rechargeable Battery System

About: After being laid off in 2009, I got rid of my car to save money. The difficult transition from a car to a bicycle led me to start Solarcycle and design USB chargers that keep smart phones alive.

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Power Stacker is a portable, modular, USB rechargeable lithium-ion battery pack. Stack them together for power hungry projects or separate them for smaller projects with this modular system. The Gerber, BOM, and .STL files are available below.

Power Stacker does what other USB rechargeable batteries have failed to do, and that's the ability to combine together for increased battery capacity or separate in to many small batteries for smaller projects. You can literally use the same Power Stacker batteries for many years across many applications!

Another unique feature of Power Stacker is that each battery receives its own charge controller, which guarantees true cell balancing and makes sure that each battery is charged to the right voltage in real-time even while charging and/or discharging.

After launching a successful Kickstarter project called Solderdoodle Pro, I realized that the same battery technology used to melt solder could be used to solve the problem of trying to find the right battery and having to constantly purchase new batteries for every new project. Combined with my knowledge of 3D printing, I created a case for the battery that can be printed, modified, and shared!

Power stacker is also compatible with Open Source DC-DC converters like Adafruit's Power Boost 1000.

How does the battery stack work?

Low forward voltage/high current diodes on the charge controller board are installed on the input and output of the circuit, which prevent cross talk between multiple power sources and between the output of the charge controllers. This allows the interconnections between the input and output pins of each charge controller board to become bus bars allowing the voltage to remain the same and the current to multiply. The highest voltage battery in the stack will discharge the most until the other batteries reach close to the same voltage and they too will begin to discharge at the same rate, which multiplies the current output of the battery pack.

Power Stacker Specs:
* Time to Fully Charge: @5 Watts 3350mAh: 3 hours | @8 Watts 13400mAh: 7 hours

* Capacity: 3350mAh, 6700mAh, or 13400mAh / 3.6V

* Type: Panasonic NCR18650B Lithium-Ion

* Input - Current: 450 to 2600mA | Voltage: 5 to 6 Volts

* Number of USB Ports: 1 (depending on the number of 5V adapter modules)

* Output - Standard Arduino Style Female and Male Headers

* Output - Current: Up to 2000mA | Voltage: 3.6 Volts direct or 5 Volts with DC-DC converter module

* Case Material: 3D printed material

* Battery Life Under Typical Use: 5 years * Replaceable Battery

* Provides up to 320% iPhone Charge or 160% Galaxy S5 Charge with two cells 6700mAh

* Compatible with Arduino, iPhone, Android, Windows Phone, and Others with 5 Volt DC-DC converter module

*WARNING: Be careful when handling any Lithium-Ion battery because shorting the battery can cause burns. Always wear safety goggles. Please use recommended battery and circuit components because of the higher 2000mA max battery charge current involved. 3D printed parts may warp under high temperatures.

FCC Compliance: NOT Required because the circuit frequencies are below 1.7MHz

Step 1: Materials, Tools, and Files Required

Here is a list of the materials, tools, and files required.


QTY Description

1 Lithium-Ion Charge Controller Circuit (Schematic, Gerber Files, etc. can be downloaded from the previous page. The main IC component is the Maxim MAX8903G charge controller.)

1 NCR18650B 3350mAh Unprotected Panasonic Lithium Ion Battery (If lower cost is necessary, try the Panasonic NCR18650A battery with a slightly less capacity of 3070mAh. Make sure it's unprotected and check the battery part number carefully. Protected batteries have added length with a built-in circuit, which may affect performance. Reference Other brands of batteries are NOT recommended because the charge controller current to the battery can be as high as 2000mA and the Panasonic NCR18650 chemistry can handle it. If you need to use other brands, make sure that they meet the same specifications, chemistry, and can handle up to 2 Amps of charge current. Using batteries that don't meet these specifications can lead to dangerous battery damage.)

2 Hirose 2-pin connector DF3-2S-2C

2 Hirose Socket 24-28 AWG Crimp Pin DF3-2428SCC

1 1" Wide Kapton Tape Roll
2 1" Kapton Tape Disc

1 1" Diameter Piece of Heat Shrink Tubing 2.7" Long
2 1/16" Piece of Heat Shrink Tubing 1.0" Long 1 Roll of solder wire 1 3D Printed case (File available on previous page.)

1 2X4 Female Header

1 5 Volt DC-DC converter

1 Protoboard

1 1X2 Female Header

1 Male Header Strip

Various Lengths 26 AWG Standard Red and Black Stranded 4 Amp Max Wire Listed Below:
1 6.10" Black Wire .06 strip one end .20 strip the other end

1 8.00" Red Wire .06 strip one end .20 strip the other end

QTY Description

1 Power Core Battery Fixture

1 Wire Strippers 24-26 gage range

1 Wire Crimper 20-24 gage range

1 Tape Measure

1 Soldering Iron

1 Heat Gun

1 Scissors

Step 2: Battery Assembly

Insert the NCR18650B battery in to the Battery Fixture with the positive side facing up. The fixture will align the Red and Black wires as you solder. Do not touch the soldering iron to the fixture because it can melt. You might be able to solder the battery without the fixture, but it is much harder and you would still need something to keep the battery from falling over. The fixture can be used for other battery projects too.

Place the .20" stripped end of the long Red wire in the trench labeled +RED and solder the Red wire to the battery. Try to solder to the battery quickly because too much heat to the battery may damage it. If there is any solder sticking out, smooth it out with the soldering iron. After soldering, tilt the fixture and push the battery out from underneath with your finger. Turn the battery upside down and insert the battery in to the fixture with the Red Wire in the +RED trough and the negative end of the battery facing up. Crimp the end of the Red wire with the Hirose Pin and insert the pin in to port 1 of the Hirose 2-Pin connector. You want to attach the connector at this point because it is dangerous to leave a dangling bare end of a battery wire exposed and can potentially cause a short or burns if it touches the negative end of the battery. Place the .20" stripped end of the long Black wire in the trench labeled -BLK and solder the Black wire to the battery. The negative end of this battery usually requires more heat to solder because there's more surface area in contact with the mass of the battery, but try to solder quick. If there is any solder sticking out, smooth it out with the soldering iron. After soldering, crimp the end of the Black wire with the Hirose Pin and insert the pin in to port 2 of the Hirose 2-Pin connector. Tilt the fixture and push the battery out from underneath with your finger. Bend the black wire straight down over the edge of the negative end of the battery and guide the red wire to loop around along the side of the battery. The effect should be that the Red wire coming down from the positive end of the battery is 120º apart from where the Black and Red wires meet. This wire geometry allows for the positive and negative wires to come out from the same side and gives the snug fit. Wrap a piece of 1" wide Kapton tape once around the middle of the battery to hold the wires down. Place a 1" Kapton tape disc at each end of the battery and fold the edges over the side of the battery. Then slide the 1" Heat Shrink Tube over the battery with the tube flush with the positive end of the battery. All the tube slack should be sticking out the negative end. Now use a heat gun to shrink the tube to complete the battery assembly.

Step 3: Power Stacker Assembly

For a single cell setup, simply solder the 2X4 Female Header to the charge controller board, connect the battery, then solder male header pins to the 5 Volt DC-DC board and connect it to the charge controller board.

For a multi-cell setup, solder the male headers to the protoboard in the same configuration as the charge controller pins and solder the 1X2 Female Header to the board.

On the back of the protoboard, solder all the pins associated with the SYS OUT port from the charge controller board, solder all the pins associated with the GND port from the charge controller board, and solder all the pins associated with the IN6V port from the charge controller board. Then solder SYS OUT to the female header pin on the protoboard and solder the GND to the other female header pin on the protoboard.

Slide the protoboard in to the slot on the 3D printed case, then attach the batteries, charge controller boards, and 5 Volt DC-DC converter to the protoboard.

Step 4: Applications

You just connect the battery to the charge controller board,
attach the DC-DC 5 Volt converter, and charge your USB device.

Connect a micro USB charge cable to recharge the batteries from
any 5 to 6 volt power source. Each cell has it’s own charge controller for true real-time cell balancing. Each charge controller in the pack will automatically start charging once excess power is detected.

You can also connect multiple energy sources to Power Stacker like solar panels, dynamos, and other USB power sources to increase the charge current to the battery pack.

Whether you’re charging a smart phone, tablet, or remote
controlled robot, Power Stacker will give you the power you need now and adapt to your power requirements in the future.

CONGRATULATIONS! Your done building the Power Stacker!

Step 5: Troubleshooting


Do Not leave Power Stacker in direct sunlight. Keep it covered or in the shade. Heat from the sun can cause the charge circuit and battery to get very hot, stop charging, degrade the battery, and shorten its lifespan.

Acceptable Temperatures: Power Stacker is designed to be operated in temperatures between 0º and 45º C (32º and 149º F). Storage: Store the Power Stacker in room temperature. Power Stacker should be recharged about once a year to prevent over discharge.

For best results, fully charge Power Stacker before using.


Power Stacker LED doesn't light up when charging from my laptop:

1) This can occur if Power Stacker is completely drained and goes in to a trickle charge mode. Keep Power Stacker plugged in for about 15 minutes and the LED charge light should turn back on.

2) Some older laptops have a low current limitation in their USB ports and will disable the USB port if the current exceeds the limit. Try plugging Power Stacker in to another USB port.

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