Source: QYM 3D 脑洞造物秦一鸣, T-15 Water Toy Gun, Bambu Store, 2024. Retrieved on Nov 11, 2025, from Bambu Store
A user can replace a lithium rechargeable battery effortlessly in just one second. But for designers, it might take days to make it truly effortless, while also ensuring safety and visual appeal. How would you approach this design? This might be a challenge many designers face in everyday practice.
Check out the battery case design in the image below. It is built for easy battery replacement.
To make this user experience possible, we need to address a few key topics in the battery case design.
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How can we make it easy for users to install and change the battery?
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How to safely keep the battery in place inside the battery case?
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How to plan the path and spacing for the battery wires to make wire connections safe and easy?
We will look at the design ideas across the following three key areas. This will help you build a battery case that looks great, works safely, and is easy to use.
Here are the three key areas we will focus on:
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Design a proper space for the battery: make room to fit safely
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Plan the spacing for battery wires: a safe space for the battery wires
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Design for airflow: let the battery ‘breathe’
We will also look at three examples: vertically and horizontally oriented battery cases, as well as side-insert designs. This will help us discuss the detailed design steps. These steps show how the earlier design ideas are used in real designs.
Now, let’s take a closer look at the design ideas.
Design ideas
1.Design a proper space for the battery
A lithium rechargeable battery has a cell, a protection circuit board, and wires. The protection circuit board keeps the battery safe from being damaged by overcharging or over-discharging. It wraps around the outside of the cell, forming a small protrusion. Differences in production processes may change where the protrusion appears. So we suggest leaving some space for the protection circuit board when designing a battery case. This helps avoid damage from pressure.
Different kinds of lithium rechargeable batteries act differently when used. For example, lithium-polymer batteries can slowly puff up if they are overcharged or drained too much. This makes the battery bigger and takes up more space. If the battery case is too small, the battery might get squeezed. This could cause it to break or short-circuit. Lithium-ion batteries have a hard shell. So they may not puff up easily. But they can still break or short out if bumped.
Considering the points above, we suggest leaving enough space for the battery when designing. Consider the following aspects to improve safety and ensure compatibility.
Avoid any sharp corners or pointy parts inside the battery case (see the image below). Such features could press against or damage the battery.
We suggest leaving extra space for the battery, in case a protrusion from the protection circuit board or a puff-up happens. The image below shows the layout of the extra space designed in the battery case.
For lithium-ion batteries, reserve about 10% of the battery’s original size as extra space around it. For a pouch-cell lithium battery, in addition to the extra space (10% of the battery’s size), along the thickness reserve about 15% of the battery’s size. This is because batteries tend to swell along their thickness. This extra space can also be used for the power wire to pass through, helping save overall space.
Getting bumped is a main risk for batteries when you use them while moving or while holding them. Please consider designing leaf springs. Leaf springs help secure the battery and keep it safe from bumps. The image below shows the leaf springs designed in the battery case.
2.Plan the spacing for battery wires
Battery wires have a core inside and an insulating layer outside. If the wires are bent too much or too often, the core may break and stop conducting electricity. It could also tear the insulating layer, causing a short circuit.
The PC003 battery wire usually uses silicone. Silicone is flexible and won’t snap easily. This prevents short circuits caused by over-bending. Even if silicone helps a lot, we still need to consider how the wires bend or get squeezed in design to avoid risks.
So, what design tips can help protect the wires from damage? How can we make a good plan for the wire path and spacing? Let’s take a look together.
We suggest keeping the wire bending radius greater than 6 times the wire’s outer diameter. The image below shows a proper bending radius design. For PC003, keep the wire bending radius greater than 12 mm. Even in the tightest space, leave a bending radius of 3 times the wire diameter for silicone wires.
The wires can be pulled or bent sharply when they go through connection points, ribs, or studs in the component (left image). Please watch the spots where plugs connect to ports or where wires go between the battery and its case. Keep in mind to avoid sharp corners or squeezing or pulling the wires in these spots (right image).
3.Design for airflow
You might notice the lithium rechargeable battery getting warm after using it for a while. This happens because the flow of electric current generates heat inside the battery. If the battery doesn’t cool down in time, the temperature inside the battery case will slowly go up. This will reduce the battery’s efficiency.
In hot or other extreme conditions, materials around the battery case may soften or lose their shape. This could cause damage. So, we suggest designing several cooling slots in the battery case to help it cool down. This is helpful for devices that stay on for a long time, like lamps. The image below shows the cooling slot design in the battery case.
Design vertically and horizontally oriented battery cases, as well as side-insert designs
You may wonder how to put the design ideas into practice. Now, let’s look at three examples together - battery cases oriented vertically and horizontally, as well as side-insert designs. All examples are a good fit for the PC003 battery. Here is how the PC003 battery looks in terms of height, width, and thickness (see the image below).
1. A vertically oriented battery case is often found in tube-shaped or portable toys. They include bubble guns, water guns, and slim remote controls.
The size of a vertically oriented battery case, for instance, is roughly 38mm x 30mm x 68mm (see the image below). It has the following features.
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It can fit the battery and the leaf springs.
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Provide a side channel for a connector to pass through, making it easy to connect to the battery at the bottom.
Usually, PC003 is about 29 mm x 16.5 mm x 51.6 mm in size (excluding the wires). Leave an extra space around the battery in all directions. This space should be 10% of the battery’s original size, which measures 32 mm x 18 mm x 57 mm. PC003 has a hard casing, ensuring its volume stability. This helps keep its shape stable and lowers the chance of swelling over time. However, we still suggest designing an extra space for the leaf springs. This approach helps reduce the possible problems caused by bumps.
Now, we need to reserve a space 6mm along its height to fit the connection of the battery wires (see the image below). This space makes it easy for the connector to pass through and helps avoid overbending the wires. If only the wire (not the connector) needs to pass through, the space can be set to 4 mm.
To stop the battery from shifting, please consider adding leaf springs on both sides. To keep the leaf springs from being too stiff and pressing hard on the battery, set the leaf spring thickness to 0.8 mm and its height to 20 mm. Please print the leaf spring parallel to the build plate. And keep the angle between the leaf spring and the battery outline between 45 and 60 degrees (see the image below).
Follow the wire layout to cut the wire channel. It should fit the wire and the power wire so that they can pass through. The image below shows the wire channel designed in the battery case.
If the battery needs to last longer, think about adding several cooling slots to the battery case walls. This will help cool it (see the image below).
At last, design the battery cover and other structures based on the requirements (see the image below).
The battery might shift if it is not held in place by snap fits along its height. To avoid the gap and cushion the impact, we can add battery springs in the battery case, similar to those used in dry cell battery cases. When you open the battery cover, the battery spring gently pushes the battery out, making it easier to remove (see the image below).
As shown in the image below, choose a spot that makes spring installation easier. First, separate the spring holders from the battery case. For removable parts like the grip, the upper side of the case is usually more suitable for installing the spring than the cover side. Attach the springs to the spring holders, then press the assembled parts into the battery case (see the image below). In the example below, the spring size is 0.5mm x 5mm x 15mm.
Please keep in mind that if the battery wires are located near the cover side, please choose springs with the proper pressure. Also, make sure to reserve enough space for the wires so they do not get squeezed (see the image below).
You could use a printed spring here for a similar effect. But over time, its elasticity weakens when kept compressed. Meanwhile, its large size may block the wire channel. So we are not giving specific examples here.
Meanwhile, to leave a larger bending radius for the battery wires, we suggest placing the battery with the protection circuit board facing outwards. The image below shows the direction the protection circuit board should face. The wires can point upwards or downwards. The leaf springs are designed for this orientation of the protection circuit board (see the image below). If the protection circuit board is turned around, small gaps may form.
We’ve made a Boolean tool for a vertically oriented battery case to help you easily build one in your design.
The dark red part in the left image below is the Boolean Tool. The right image below shows the battery case made using the Boolean Tool.
In your CAD software, first import the Boolean Tool and place it where you want the battery case to be. Once it is lined up, use a feature like Modifiers in Blender or Combine in other CAD software to carve out the shape from the main part. This creates the battery case. After that, modify it to fit with the other parts.
2. A horizontally oriented battery case is often found in the chassis of model cars or at the bottom of models, like remote-controlled cars and table decorations.
The size of a horizontally oriented battery case, for instance, is roughly 36 mm x 19 mm x 56 mm. It has the following features (excluding the space for the wires positioned on the top).
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It can fit the battery and the snap fits.
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It gives the side wall room to bend or flex. (see the image below)
Horizontally oriented battery cases are usually used in setups with more space. Meanwhile, this layout offers more ways to arrange battery wires. Therefore, the provided size does not include the extra height required for the horizontally oriented battery.
When installing and removing the battery, the snap fits on both sides may bend outward. So, we need to leave space on the outer side of the battery case for the snap fits. These will hold the battery in place (see the image below).
To design a horizontally oriented battery case, first we need to draw the case bottom, then the snap fits to hold the battery in place.
First, draw the case bottom. Please draw an oval track, sized 32 mm x 18 mm x 52 mm. Set the case bottom to 10 mm in depth and add 2 mm-thick walls along the battery’s height (see the image below).
When the design requires embedding the screw head at the bottom of the case, it must avoid getting in the way of the battery. So, the bottom structure should be designed with installation needs in mind. We take the M2.5 button head cap machine screws as an example. Its head is about 4.7 mm in diameter and 1.5 mm in thickness. So, we need to make the case bottom thicker by 2 mm. Then add two countersunk screw holes with a 5 mm diameter and 2 mm depth, each with a 2.8 mm through-hole (see the image below).
On the side of the battery case, we need snap fits to hold the battery in place. Therefore, we need to set the top edge of the battery case to 1.2 mm and its bottom edge to 2 mm (see the image below). For bigger and heavier batteries, we can make the snap fits wider at the top to get a stronger structure.
Now, let’s draw the snap fits to hold the battery. The battery’s cross-section is not a uniform oval track because of the protection circuit board. Therefore, the direction that the protection circuit board faces affects the height of the snap fits. So we need to design the snap fits differently to suit the two cases below.
When the protection circuit board faces upward
When the protection circuit board and the wires are placed on top, make the oval track 29 mm wide and 14 mm high. The snap fits shall connect to the upper half of the oval track and extend 2.4 mm to 3 mm beyond the battery’s widest section (see the image below). The extended part shall roughly cover half of the battery’s curved surface. Place the snap fits at the center of the case’s side walls and set their width to 10 mm. Apply a fillet of R0.4 to the sharp edges at the top and bottom of the snap fits. This keeps the battery safe from being damaged by pressure (see the image below).
When the protection circuit board faces downward
When the protection circuit board and the wires are placed at the bottom, make the oval track 29 mm wide and 16.5 mm high (see the image below). Compared to the case where the protection circuit board and wires are at the top, the oval track is 2.5 mm higher.
To ensure optimal snap fit strength, we suggest printing the battery case upright, keeping the snap fits parallel to the build plate. Cut both sides of the snap fits and chamfer them at an angle of 55° - 65° (see the image below). This helps minimize support structures and sets the snap fits and case walls apart.
If the wires point downward, make a wire slot at the front and the back. The slot should be 10 mm wide and 6 mm high to let the connector through (see the image below).
If you are using batteries in fast or bumpy situations (for example, a high-speed RC car), they may not be firmly fixed with snap fits alone. During a crash, the battery could easily fall out. So, we suggest adding hollow grips on both sides of the snap fits. Then, you can fix the battery to the case with velcro straps (see the image below).
Another option is to reserve extra space at the bottom of the battery case. Then, place velcro straps on both the case and the battery to fix them firmly. Also, make sure the battery case faces the same way as the wires and place the case at the front or back of the model. So the battery is less likely to pop out.
3. A side-insert battery case is often found at the bottom of models, saving space horizontally.
We can install the battery sideways to save space and stay flush with other components. This setup holds the battery more safely than the horizontally oriented battery case. So it won’t fall out easily. The size of a side-insert battery case, for instance, is roughly 24.5 mm x 35 mm x 85 mm. It has the following features.
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It can fit the battery and the snap fits.
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It gives the side wall room to bend or flex (see the image below).
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It includes a grip zone to help remove the battery from the front and back (see the image below).
When designing a side-insert battery case, we also need to create a rough base and reserve space for the battery (left image). Attention please: the protection circuit board sits on one side of the battery. Still, we need to reserve space on both sides for installing snap fits.
We suggest reserving space on both sides for the protection circuit board, which is 22 mm high and 1.55 mm wide (right image). Set the side walls of the case to 1.2 mm thick, preparing for adding snap fits (right image). And set the front and the back walls to 1.6 mm thick, and the bottom to 2 mm thick.
At the center of the case’s side walls, set the snap fits to 18 mm and trim the excess material from both sides. After cutting away the excess material, add a 20° chamfer to both ends of the snap fits. This helps minimise the need for support structures. And add a 1 mm chamfer to the snap fit openings. This makes installing the battery easier.
Trim the excess material off both sides of the part where the wires will pass (see the image below). This forms a clean path for the battery wires to pass through.
Smooth out the edges around the battery case to keep your hands from getting scratched.
Similar to the design of the horizontally oriented battery case, make the case bottom 2 mm thicker and add countersunk screw holes.
To help users replace lithium rechargeable batteries more easily, we’ve broken down the battery case design into three aspects: designing a proper space for the battery, planning the spacing for battery wires, and designing for airflow. We’ve shared design ideas, steps, and tips for battery cases oriented vertically and horizontally, as well as side-insert designs. We hope this article provides helpful guidance and new ideas for your projects.
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If this guide sparked ideas or felt familiar, share your thoughts in the comments — let’s chat! Like and save if it helped.