DURACELL Max

Greetings, everyone, and welcome back!

Here’s something biblically large. Meet DURACELL MAX, a giant Duracell battery that I made completely from scratch.

The idea behind this project was to build an emergency power source capable of providing a stable 12V output for various applications, such as driving an e-bike DC motor or powering other electronics projects.

I also included two separate 65W USB-C PD modules. Using a USB-C to USB-C cable, we can charge smartphones, tablets, handheld gaming consoles, and even laptops. This makes the battery pack a useful tool during a blackout, and it can also be carried on camping trips to charge devices or power 12V light sources and other equipment.

For the design of this project, I wanted to create something truly different from a regular battery pack enclosure. So, I modeled the entire battery pack to look like a ridiculously oversized Duracell AA battery.

Inside the enclosure is a custom-made battery pack built using LiFePO4 cells arranged in a 4S6P configuration. The completed battery pack has a nominal voltage of approximately 13.3V, a capacity of 36Ah, and stores roughly 470Wh of energy.

This Article covers the complete build process of this project. So, without further ado, let’s get started!

MATERIAL REQUIRED

These were the materials used in this project—

• LiFePO4 Cells 3.3V 6000mAh
• 3D Printed Parts
• Custom PCBs
• M2 Screws
• Nickel Strip 8mm Width
• Spot Welder
• PD Modules 65W Output
• BMS LiFePO4 Cell 4S
• Connecting Wires
• Toggle Switch
• DC Barrel Jack
• 3mm LED RED
• Diode SR206
• 10K Resistor
• 12V 5A Charger
• E-Bike Motor 250W (for Demo)
• 12V HDMI Display (for Demo)
• Multimeter
• M4 Nut and Bolt
• Banana Pin Connector

HARDWARE- LiFePO4 CELLS

The main power source for this project is a set of LiFePO4 (Lithium Iron Phosphate) cells, each rated at 3.3V and 6000mAh. LiFePO4 cells are a great choice for this type of project because of their long cycle life, good thermal stability, and relatively safe chemistry compared to many other lithium battery types.

For this project, the idea is to build a 4S6P battery pack. This means six cells are first connected in parallel to increase the overall capacity, and four of these parallel groups are then connected in series to increase the pack voltage. In total, the battery pack uses 24 LiFePO4 cells.

Before assembling the battery pack, I checked the voltage of every individual cell using a multimeter and sorted them into groups with closely matched voltages. The cells used in this project were between approximately 3.270V and 3.280V.

Matching the cell voltages is especially important before connecting cells in parallel. When two cells with different voltages are directly connected in parallel, the higher-voltage cell will immediately start supplying current to the lower-voltage cell. Since lithium cells have very low internal resistance, even a relatively small voltage difference can potentially result in a high equalization current, causing excessive heat and creating a serious safety hazard.

Once cells are permanently connected in parallel, they behave electrically as a single, higher-capacity cell group because all the cells share the same voltage.

Series-connected groups work differently. In our 4S configuration, each parallel group can have a different voltage from the others because the BMS individually monitors the voltage of each series group through its balance connections. During charging, the BMS helps prevent individual series groups from exceeding their safe voltage limits and, if the BMS supports active or passive balancing, helps keep the series groups balanced.

However, the BMS cannot individually monitor or control each cell inside a parallel group. This is why checking and closely matching the voltage of all cells before connecting them in parallel is an important step in building the battery pack safely.

After checking all 24 cells and confirming that their voltages were within the required range, they were ready to be arranged inside the custom battery holders and connected to form the 4S6P battery pack.

HARDWARE- BMS

For managing and protecting the battery pack, I am using a 4S 20A BMS specifically designed for LiFePO4 cells. The BMS supports a 4S configuration with a nominal pack voltage of 12.8V and a continuous discharge current of up to 20A.

The main purpose of the BMS is to protect the LiFePO4 cells during charging and discharging. It provides essential safety features, including overcharge, over-discharge, overcurrent, and short-circuit protection.

The BMS continuously monitors the voltage of each series cell group and disconnects the battery pack if the voltage exceeds or drops below the safe operating limits.

With its 20A continuous discharge capability, this BMS is suitable for our 4S6P battery pack and allows us to safely charge the battery and power various devices connected to the output.

HARDWARE- PD MODULE

For the USB-C power output, I am using a 65W PD fast-charging module. This is a compact and highly efficient DC-DC step-down converter that supports multiple fast-charging protocols, including PD3.1 (PPS), QC3.0, Huawei SCP/FCP, and Samsung AFC.

The module accepts an input voltage of 8V to 30V and can provide up to 65W of output power through the USB-C port. It features intelligent PD negotiation, which automatically adjusts the output voltage between 3.3V and 21V according to the requirements of the connected device.

With a conversion efficiency of around 92–97%, the module produces minimal power loss and heat. It also includes built-in over-voltage, under-voltage, short-circuit, and over-temperature protection.

Its compact 32x20mm size makes it perfect for integrating into our giant battery pack and allows us to charge smartphones, tablets, handheld gaming consoles, and even PD-compatible laptops.

I found this really good guide on the internals of this PD Module, its schematic, and other working details.

https://www.beyondlogic.org/review-usb-pd-65w-fast-charging-module-xpm52c/

DESIGN

For the design of this project, my plan was to model the battery pack after a Duracell AA cell. However, instead of completely replicating the original design, I only used its basic cylindrical shape and appearance as inspiration. The rest of the parts were designed from scratch based on the specific requirements of the project.

I started by designing an internal battery holder that holds six cells in a parallel configuration. Four of these battery holders are then stacked together to form the complete cylindrical 4S6P battery pack assembly.

The Duracell-inspired outer enclosure is essentially a cover that fits around the cylindrical battery assembly. The top section was also designed to resemble the positive terminal of a regular AA cell. This section houses two banana plug connectors and a DC barrel jack for the main power connections.

On the front of the enclosure, I also added two USB Type-C openings for the dual 65W PD modules, allowing us to connect and charge USB-C PD-compatible devices directly from the battery pack.

The entire enclosure and internal assembly were designed from scratch using Fusion 360, with each part modeled around the dimensions and requirements of the battery cells, electronics, and output connectors.

CELL HOLDER

The core part of this project is the cell holder, which was designed to hold six LiFePO4 cells in a hexagonal arrangement.

The holder mainly consists of three parts: the top holder, the bottom holder, and four mid-support pieces. These mid-support pieces are placed between the top and bottom holders, and M2.5 screws are used to secure the top holder to the mid supports and the bottom holder to the mid supports. This assembly securely holds the LiFePO4 cells in place.

The top and bottom holders are open on one side, allowing access to the cell terminals. This exposed side is required so that nickel strips can be spot-welded to the cells, connecting all six cells in parallel. I also designed a custom hexagonal nickel strip, which I will make using standard nickel strips and a 3D-printed jig.

On both the top and bottom holders, I added a PCB that is soldered to the nickel strips. These PCBs are used to connect multiple cell holders together, allowing all four parallel groups to be connected in series.

CELL HOLDER GROUP

Once all four cell holders are assembled, they are stacked one above the other to form the complete battery pack. M4 nuts and bolts are then used to secure the assembly while simultaneously connecting the PCBs of adjacent cell holders. These PCB connections link the positive terminal of one cell holder to the negative terminal of the next, creating a 4-series (4S) battery pack.

The final result is a large cylindrical battery pack consisting of four cell holders connected in series. Each cell holder contains six LiFePO4 cells connected in parallel using the custom hexagonal nickel strips and connection PCBs, resulting in a complete 4S6P battery pack.

DURACELL SHELL & TOP PART

Next comes the outer shell, which mainly consists of three parts: the base, the Duracell shell, and the upper section.

Starting from the bottom, the base is attached to the battery pack assembly using four M2 screws, securing it to the bottom of the cell holder group. The Duracell shell then slides into position over the cylindrical battery pack and is held in place by the base. Finally, the upper section slides into place above the Duracell shell, completing the main body of the enclosure.

The top assembly is made up of two parts: an inner support and the top cover itself. The inner support is responsible for holding the 65W PD modules, the BMS, and most of the internal wiring, keeping all the electronics securely organized.

Also, we have added an opening for the Type C port in this inner support part and also a slide switch for turning the PD Module ON or OFF.

The top cover acts as the lid of the entire assembly and houses the main input and output connectors. For power output, I added two banana plug connectors, allowing the battery pack to power various external devices. A standard DC barrel jack is also included for charging the battery pack, along with an indicator LED that lights up whenever the charger is connected.

Besides housing the connectors, the top cover also locks the Duracell shell and the upper section in place. In combination with the base, it effectively sandwiches the entire enclosure together, keeping all the internal components securely assembled without any movement.

3D PRINTED PARTS

After finalizing the 3D model, all the parts were exported as mesh files and 3D-printed on our Anycubic Kobra S1 printer. I used white, grey, and dual-tone Hyper PLA filaments for the different parts of the enclosure.

All parts were printed using a 0.2mm layer height, a 0.4mm nozzle, and 25% infill.

For the parts that required support, I mostly used tree supports with a 0.3mm top Z distance. This provided enough clearance between the supports and the printed parts, making the supports relatively easy to remove after printing.

PCB DESIGN

Following the board outline from my CAD model, I designed the connection PCB for this project. There is nothing particularly complex about this board—it is essentially a simple PCB with a large copper pour used to carry the battery current.

The PCB includes several slots where the custom nickel strips are inserted and soldered, along with mounting holes that allow it to be securely fixed to the cell holder.

Since the shape of the PCB is quite unconventional, I first exported the board outline as a DXF file from Fusion 360. I then imported this DXF into my PCB design software and used it as the board outline. This ensured that all the mounting holes and nickel strip slots were positioned exactly as designed in the CAD model, eliminating any alignment issues during assembly.

To simplify the assembly process, I added a + symbol on the top silkscreen layer and a − symbol on the bottom silkscreen layer. When mounting the PCB on the positive side of a cell holder, the side with the + marking faces upward. Likewise, when mounting it on the negative side, the PCB is flipped so that the − marking faces upward. This simple orientation system makes it much easier to identify the polarity of each cell holder and simplifies connecting all four holders together in series.

NextPCB SERVICE

Gerber data for the PCB was sent to HQ NextPCB, and an order was placed for a Black solder mask and white silkscreen.

After placing the order, the PCBs were received within a week, and the PCB quality was pretty great.

In addition, I have to bring in HQDFM to you, which has helped me a lot through many projects. Huaqiu’s in-house engineers developed the free Design for Manufacturing software, HQDFM, revolutionizing how PCB designers visualize and verify their designs.

Take advantage of NextPCB's Accelerator campaign and get 2 free assembled RP2040-based PCBs for your innovative projects.

https://www.nextpcb.com/blog/rp2040-free-pcba-prototypes-nextpcb-accelerator

This offer covers all costs, including logistics, making it easier and more affordable to bring your ideas to life. SMT services can be expensive, but NextPCB is here to help you overcome that hurdle. Simply share your relevant project, and they'll take care of the rest. Don't miss out on this amazing opportunity to advance your tech creations!

HQDFM: Free Online Gerber Viewer and DFM Analysis Tool

Also, NextPCB has its own Gerber Viewer and DFM analysis software.

Your designs are improved by their HQDFM software (DFM) services. Since I find it annoying to wait for DFM reports from manufacturers, HQDFM is the most efficient way to perform a pre-event self-check.

This is what I see in the online Gerber Viewer. It's decent for a quick look, but not entirely clear. For full functionality—like detailed DFM analysis for PCBA—you’ll need to download the desktop software. The web version only offers a basic DFM report.

With comprehensive Design for Manufacture (DFM) analysis features, HQDFM is a free, sophisticated online PCB Gerber file viewer.

With over 15 years of industry experience, it offers valuable insights into advanced manufacturing processes. If you’re looking for reliable PCB services at a budget-friendly price, HQ NextPCB is definitely worth checking out.

NICKEL STRIP ASSEMBLY

For connecting the cells in parallel, the best method is to use a spot welder with nickel strips.

Directly soldering wires or strips to the terminals of lithium cells is generally considered bad practice, as the excessive heat generated during soldering can damage the cells, reduce their capacity, or, in extreme cases, create a serious safety hazard. This is why spot welding is commonly used for assembling lithium battery packs.

One challenge I faced was that, because of the unusual cell arrangement used in this project, standard nickel strips would not work well. Therefore, I had to design a custom hexagonal nickel strip setup.

For the spot-welding process, I got myself a portable spot welder.

• The process begins by cutting the nickel strips into two different sizes, as mentioned in the Strip Size PDF. The longer 39mm strips are used to create the hexagonal shape for connecting the cells, while the smaller 10mm strips are used to create the L-shaped section that will allow us to mount the PCB above the nickel strip.
• Using a custom 3D-printed jig, we first place the 39mm nickel strips into their designated slots to form a hexagonal shape. The second half of the jig is then placed on top to hold all the strips securely in position.
• Next, using the portable spot welder, we spot-weld all the individual strips together, resulting in a single hexagonal nickel strip.
• We then place the L-shaped section in its designated position on top of the hexagonal nickel strip.
• The second half of the jig is placed over the entire setup to hold everything securely in position, and the L-shaped section is spot-welded to the hexagonal nickel strip.

The result of this process is a custom hexagonal nickel strip that will be used to create the parallel connections in our battery pack.

For this project, we need a total of eight custom hexagonal nickel strips.

PARALLEL PACK ASSEMBLY

• We begin the assembly process by first installing the four mid-support pieces onto the bottom cell holder and securing them in place using M2 screws.
• Next, the LiFePO4 cells are inserted into the bottom holder with the negative terminals facing downward and the positive terminals facing upward.
• The top cell holder is then placed over the cells and secured to the mid-support pieces using M2 screws. This firmly locks all six cells in place, completing the mechanical assembly of one parallel cell holder.
• The electrical connections are made next. We begin by placing the custom hexagonal nickel strip on the positive side of the cell holder. Using a spot welder, the nickel strip is welded to the terminals of all six cells, electrically connecting them in parallel.
• The same process is then repeated on the negative side of the battery pack using another hexagonal nickel strip.
• Once both nickel strips are spot-welded, the connection PCBs are placed over the nickel strips and secured using M2 screws. Finally, the nickel strips are soldered to the PCBs, creating a solid electrical connection between the cells and the connection boards.
• The same process is done on both the positive and negative sides of the cell holder, completing one fully assembled parallel battery module.

TEST

To verify that everything was assembled correctly, I measured the output voltage of the completed parallel cell holder using a multimeter. The measured voltage was approximately 3.27V, confirming that all six cells were properly connected in parallel and the assembly was functioning as expected.

Since the final battery pack requires four identical parallel cell holders, I repeated the entire assembly process three more times until all four modules were complete and ready to be connected in series.

COMBINED PACK ASSEMBLY

Now comes the main assembly of the battery pack.

• The process begins by stacking all four parallel cell holders on top of one another in the correct orientation, as shown in the assembly diagram.
• To electrically connect the four modules in series, M4 nuts and bolts are used to fasten the connection PCBs together. These connections link the positive terminal of one parallel pack to the negative terminal of the next, completing the 4-series (4S) configuration.

Once all four modules are connected, the battery pack has a nominal output voltage of approximately 13.3V. The positive output terminal is located at the topmost cell holder, while the negative output terminal is located at the bottommost cell holder, making these the main output terminals of the completed battery pack.

WIRING

• We begin the wiring process by connecting wires to each parallel cell holder according to the provided wiring diagram.
• The wires are soldered to the connection PCB of each parallel pack and then routed through the opening in the center of the cell holder. All of the wires are passed through this central opening, where they will later be connected to the BMS.

For the power connections, I am using 16 AWG single-core copper wire, which is capable of handling currents well above the requirements of this project while keeping voltage drop and heat generation to a minimum. Using thicker wire also makes the battery pack more reliable when powering higher-current loads.

TOP LID ASSEMBLY

• The assembly of the top cover begins by installing the red and black banana connectors into their respective mounting holes. Both connectors are inserted from the outside of the top cover and positioned correctly.
• Next, a red and a black wire are soldered to the solder lugs of the banana connectors. The wires are then routed through the openings inside the top cover, and the supplied mounting nuts are tightened to securely lock both banana connectors in place.
• The DC barrel jack is installed next and secured using its supplied mounting nut.
• For the wiring, the VCC terminal of the DC barrel jack is connected to the cathode of an SR206 Schottky diode, while the anode of the diode is connected to the red banana connector. The GND terminal of the DC barrel jack is connected directly to the black banana connector.
• Next, a 3mm LED is installed in its mounting hole. The anode of the LED is connected to the VCC terminal of the DC barrel jack before the diode. This ensures that the LED only illuminates when a charger is plugged into the DC jack.
• Finally, a 10kΩ resistor is soldered between the cathode of the LED and the GND terminal of the DC barrel jack, completing the charging indicator circuit.

OUTER SHELL ASSEMBLY

• We begin the outer shell assembly by placing the base onto the bottom of the battery pack and securing it using four M2 screws.
• The battery pack is then turned over, and the Duracell shell is slid into position over the cylindrical battery pack. Once the Duracell shell is in place, the upper shell is also slid into its designated position.
• Next, the inner support is installed at the top of the battery pack and secured using M2 screws. This inner support not only provides a mounting point for the electronics but also locks the upper shell and Duracell shell in place, keeping the entire outer enclosure securely assembled.

FINAL ASSEMBLY

• We begin the final assembly process by mounting the BMS inside the inner support part. To secure it in place, I applied a piece of double-sided thermal tape and then placed the BMS on top. The thermal tape keeps the BMS firmly attached while also helping transfer heat to the mounting surface.
• Next, by following the wiring diagram, the BMS is connected to the battery pack. The B- terminal is connected to the battery negative, B1 to the 3.3V tap, B2 to the 6.6V tap, B3 to the 9.9V tap, and B+ to the 13.2V positive terminal of the battery pack.
• The two 65W USB-C PD modules are then installed. Thermal tape is applied beneath each module before placing it into its respective position.
• After that, the lever switch is installed just above the PD modules and secured using the supplied mounting nut.
• The wiring of the PD modules is fairly straightforward. First, the VIN and GND terminals of both PD modules are connected in parallel. The combined VIN connection is then connected to the P+ terminal of the BMS.
• For the negative connection, the combined GND terminals of both PD modules are connected to the COM terminal of the lever switch, while the NC terminal of the switch is connected to the P- terminal of the BMS. In other words, the switch is placed in series with the negative supply line, allowing it to connect or disconnect power to both PD modules simultaneously.
• Finally, the pre-assembled top cover is connected to the battery pack by soldering the red wire from the banana connector to the P+ terminal of the BMS and the black wire to the P- terminal.
• With all the wiring complete, the top cover is positioned onto the enclosure and secured using five M2.5 screws. This locks the entire assembly together and completes the final assembly of the giant Duracell battery pack.

RESULT

And here's the final result of this giga build—a Duracell battery that is definitely not AA-sized!

The completed battery pack weighs around 4.7kg and provides a stable 13.2V output, making it suitable for powering a wide range of 12V devices and DIY electronics projects.

Thanks to the onboard dual 65W USB-C PD modules, it can also be used as a portable power bank for charging PD-compatible devices such as smartphones, tablets, handheld gaming consoles, and even laptops.

WORKING DEMO

To test the battery pack in the real world, I first connected a 12V monitor that I had previously disassembled for an upcoming project. Using a pair of banana cables, I connected the monitor's driver board to the battery pack's output terminals, and the display powered on and worked perfectly.

Next, I tested the onboard USB-C PD modules by connecting my MacBook with a USB-C-to-USB-C cable. The laptop started charging immediately without any issues.

I then repeated the same test with my ROG Ally, and it also charged normally through the PD module.

Finally, I connected a 250W e-bike motor directly to the battery pack's output. As expected, the motor ran without any problems, confirming that the battery pack can comfortably power higher-current 12V loads.

For charging the battery pack, I used a 12V 5A charger capable of delivering approximately 60W of charging power. Since the battery pack has a capacity of roughly 470Wh, a full charge takes around 8 hours with this charger.

The charging time can be reduced by using a higher-current power supply, such as a 12V 10A charger. Another option is to charge the battery pack using a solar panel. Since the BMS used in this project can tolerate charging input voltages of up to 45V, a solar panel with an open-circuit voltage below this limit can be connected. For example, a 24V, 4A (approximately 100W) solar panel would be an excellent choice for charging this battery pack outdoors.

CONCLUSION

Overall, this was a really fun project to build. My favorite part was designing the outer enclosure and adding the cosmetic details that transform an ordinary cylindrical battery pack into what looks like a ridiculously oversized Duracell AA battery.

That said, I already have a few ideas for Version 2 of this project.

The first upgrade I'd like to add is a custom ESP32-based control board with a built-in display. This would provide real-time information such as battery voltage, remaining capacity, charge and discharge current, power consumption, individual cell voltages, temperature, and charging status. It could also be used to monitor solar charging and make the battery pack much more informative to use.

The second upgrade I'd like to explore is integrating an MPPT solar charge controller. This would allow the battery pack to function as a true portable solar power station, capable of efficiently charging directly from solar panels. Paired with a DC-to-AC inverter, the system could even provide AC power, making it a much more versatile backup power solution.

For now, though, this project is complete, and I'm really happy with how it turned out. I hope you enjoyed following along with the build as much as I enjoyed designing and building it.

Peace!