Connecting 3.7 Volt Lithium Batteries for Custom Voltage Needs

You can achieve custom voltage and capacity by connecting 3.7 volt lithium batteries in series, parallel, or a combination of both. Series increases voltage, while parallel boosts capacity. Always match the voltage and capacity of each battery before you connect lithium batteries. Use a battery management system (BMS) for protection. Check your wiring carefully, because connecting 3.7 volt lithium batteries incorrectly can cause serious safety incidents:

• 短路
• Fires or explosions
• 过度充电
• 机械损坏
• Failures from defective battery cells

Learning how to connect lithium batteries safely protects you and your devices.

Connecting 3.7 Volt Lithium Batteries

When you want to build a custom lithium battery pack, you can use three main methods: series connection, parallel connection, and series and parallel connection. Each method changes the voltage and capacity of your pack in different ways. You must always match the voltage, capacity, and state of charge of each battery before connecting 3.7 volt lithium batteries. Using a battery management system (BMS) helps keep your pack safe and balanced.

Series Connection

A series connection links the positive terminal of one battery to the negative terminal of the next. You keep connecting batteries in series until you reach the voltage you need. The total terminal voltage of the pack is the sum of each battery’s voltage, but the capacity stays the same as one battery.

• For example, if you connect two 3.7V 100mAh batteries in series, you get 7.4V at 100mAh.
• This method works well for devices that need higher voltage than a single cell can give.
• After you connect in series, the two free terminals (one positive, one negative) become the output for your lithium battery pack.

小贴士 Always use batteries in series that have the same voltage, capacity, and charge level. If you mix them, you can cause imbalances, reduce performance, or even damage the pack.

You should check the total voltage with a multimeter after connecting batteries in series. If you see a voltage that does not match your calculation, check your wiring. A BMS is important for series connection because it helps balance the cells and prevents overcharging or deep discharging.

Parallel Connection

A parallel connection joins all the positive terminals together and all the negative terminals together. When connecting batteries in parallel, the voltage stays the same as one battery, but the capacity adds up. This means your pack can run longer and supply more current.

• For example, if you connect two 3.7V 100mAh batteries in parallel, you still get 3.7V, but now you have 200mAh.
• Parallel connection increases the total current output and extends the runtime of your lithium battery pack.
• If one battery fails, it only reduces the capacity, not the whole pack’s function.

请注意： Only connect batteries in parallel if they have the same voltage and capacity. If you mix batteries, you risk overcharging, overheating, or damaging the pack. Always use fuse protection and a BMS to keep your pack safe.

Parallel connection also reduces internal resistance, which helps your pack deliver more power. However, differences in internal resistance or heat can shorten the life of your pack. Always check that each battery matches before you connect in parallel.

Series and Parallel Connection

A series and parallel connection combines both methods. You first connect groups of batteries in parallel, then connect those groups in series, or vice versa. This setup lets you build a lithium battery pack with both higher voltage and higher capacity.

• For example, you can make two parallel groups of two 3.7V 100mAh batteries each. Then, connect those groups in series. The result is a pack with 7.4V and 200mAh.
• This series-parallel connection is common in custom packs for electric bikes, power tools, and backup systems.

警告 Series-parallel connection needs careful matching. Each battery must have almost the same voltage (within 10mV), capacity (within 20mAh), and internal resistance (within 5mΩ). If you mix batteries of different brands, ages, or types, you risk fire, damage, or loss of capacity.

You must use a BMS or protection circuit module for every battery in a series-parallel connection. The assembly process includes sorting, welding, insulation, and testing. Always check the voltage and capacity of each cell before building your pack. If you skip these steps, you can cause deep discharge, overcharge, or even fire.

Key Point: Never mix batteries with different voltages or capacities in a series-parallel connection. Always balance and test your pack before use. A BMS is not optional—it is required for safety.

A well-built series and parallel connection gives you the custom voltage and capacity you need. It also keeps your lithium battery pack safe and reliable for your project.

Series and Parallel Battery Configurations

When to Use Series

You use batteries in series when your device needs increased voltage. This method connects the positive terminal of one battery to the negative terminal of the next. Many electric vehicles, laptops, and home energy storage systems rely on series and parallel battery configurations to reach the right voltage. For example:

• Electric vehicles often use 10 or more batteries in series to reach 36V or 72V.
• Laptops use 3 or 4 batteries in series for better efficiency.
• Home backup systems may use 14 or more batteries in series to match inverter requirements.

"(《世界人权宣言》) table below shows how the voltage increases as you add more batteries in series:

If you wire batteries in series incorrectly, you risk short circuits, overheating, or even fire. Always match the voltage and capacity of each battery in your pack.

When to Use Parallel

You use batteries in parallel when you want increased capacity and longer runtime at the same voltage. This setup is best for devices that need to last longer without raising voltage, like solar-powered LED lights or portable electronics. In a parallel connection, the pack can keep working even if one battery fails, which improves reliability.

1. Parallel connection keeps the voltage at 3.7V but adds up the capacity of each battery.
2. Devices that need more energy storage, such as backup power systems or power banks, benefit from this setup.
3. The current load spreads across all batteries, reducing heat and stress, which helps your lithium battery pack last longer.

If you do not match the internal resistance and charge level of each battery, you can cause overheating or reduce the pack’s lifespan. Always use batteries from the same batch for best results.

When to Combine Both

You combine series and parallel connection when your project needs both increased voltage and increased capacity. This combination of series and parallel connections is common in custom lithium battery pack designs for renewable energy storage, electric bikes, and power tools. With this method, you can build a pack that meets your exact voltage and energy needs.

• Series connections give you the voltage you need.
• Parallel connections give you the capacity and runtime you want.
• Together, series and parallel battery configurations offer flexibility and reliability.

However, wiring errors can cause serious problems. Loose connections, mismatched batteries, or poor assembly can lead to current imbalance, overheating, or even thermal runaway. Always check every connection and use a battery management system to keep your lithium battery pack safe.

How to Connect Lithium Batteries

Materials Needed

Before you start learning how to connect lithium batteries, gather all the right tools and materials. You need these items to connect lithium batteries safely and build a reliable battery pack:

• 3.7V lithium battery cells (all with the same voltage and capacity)
• Soldering iron (at least 30 watts) and quality rosin core solder
• Pure nickel strips for strong connections
• Spot welder (preferred for nickel strips)
• Digital multimeter for checking voltage and connections
• Wire strippers, side cutters, and a sharp knife
• Battery holders or spacers for stability and insulation
• Battery Management System (BMS) for protection
• Balance connectors and wires (26 gauge for balance, 18 gauge for main current)
• Connectors like XT60 or Deans T-type
• Heat shrink tubing, masking tape, or electrical tape for insulation
• Safety gear such as gloves and goggles

小贴士 Always use a balance charger to keep your battery cells healthy and balanced.

Wiring Steps

Follow these steps to learn how to connect lithium batteries in series, parallel, or series-parallel:

1. Check each battery with a multimeter. Make sure all voltages match closely before you connect lithium batteries.
2. For series connection, link the positive terminal of one battery to the negative terminal of the next. Continue until you reach the voltage you want. The two free terminals become your output.
3. For parallel connection, join all positive terminals together and all negative terminals together. This keeps the voltage the same but increases the capacity.
4. For series-parallel, first make parallel groups, then connect those groups in series. This method lets you build a battery pack with custom voltage and capacity.
5. Use nickel strips and spot welding for strong, safe connections. If you must solder, work quickly to avoid overheating the battery.
6. Attach the BMS to the battery pack. Connect the balance leads to each cell group.
7. Insulate all connections with heat shrink tubing or electrical tape.
8. Use a multimeter again to check the total voltage and make sure all connections are secure.

请注意： Always double-check polarity. Reversing wires can damage your battery or cause a fire.

Safety Checks

You must perform safety checks every time you connect lithium batteries. These steps help prevent accidents and keep your battery pack safe:

⚠️ Never connect lithium batteries with different voltages or damaged cells. This can cause overheating, fire, or even explosions.

If you follow these steps on how to connect lithium batteries, you will build a safe and reliable battery pack for your project.

Choosing the Right Series and Parallel Connection

Matching Voltage to Device

You need to match your battery pack’s voltage to your device’s requirements. Start by checking the device label or manual for the desired operating voltage. If your device needs more voltage than a single 3.7V battery can provide, you should connect batteries in series. Each battery you add in series increases the total voltage, but the capacity stays the same.

• Series connection works best for devices like electric bikes, medical equipment, or backup systems that need higher voltage.
• Always use batteries with the same voltage, age, and health in a series pack.
• Use a battery management system (BMS) that monitors each cell to keep your battery pack safe.
• Regularly check each battery’s voltage to avoid imbalances.

Here is a simple way to calculate the number of batteries you need in series:

Tip: Always round up if your device’s voltage is not an exact multiple of 3.7V.

Matching Capacity to Needs

If your device needs to run longer or supply more current, you should focus on increasing battery capacity. Connect batteries in parallel to add up their capacities while keeping the voltage the same.

• Parallel connection is ideal for power banks, solar lights, or any device that needs longer runtime.
• Make sure each battery has nearly the same voltage before connecting in parallel.
• Use thick, equal-length wires to balance resistance and keep your battery pack safe.
• A BMS designed for parallel setups helps protect against overcharging and overheating.

To find out how many batteries you need in parallel, divide your device’s required capacity by the capacity of one battery. For example, if your device needs 2000mAh and each battery is 1000mAh, you need two batteries in parallel.

Note: For custom packs, you can combine series and parallel connections to reach both the voltage and capacity your device needs.

Connect Lithium Batteries Safely

常见错误

You can avoid many problems by learning about the most common mistakes people make when connecting a battery pack. Mixing old and new batteries often causes imbalance and poor performance. If you connect batteries with different amp-hour ratings in series, the smaller battery may over-discharge, which can lead to overheating or even fire. Ignoring the need for a Battery Management System (BMS) is another big mistake. Without a BMS, you risk uneven charging and discharging, which can cause some cells to overcharge and others to reverse charge. This can make a battery fail early or even burst. Using undersized cables can cause voltage drops and overheating. Incorrect wiring, such as reversing polarity or connecting batteries with mismatched voltages, can damage the battery and your device.

⚠️ Never ignore BMS alerts or warnings. Most battery failures happen because people do not pay attention to these signals.

Here are some mistakes you should avoid:

• Mixing old and new batteries in one pack
• Ignoring BMS alerts or skipping BMS installation
• Using cables that are too thin for the current
• Connecting batteries with different capacities in series
• Not checking each battery’s voltage before assembly
• Poor welding or loose connections

Safety Tips

You can keep your battery pack safe by following some simple safety tips. Always use a BMS to monitor temperature, voltage, and current. The BMS acts as the brain of your battery, protecting it from overcharging, deep discharging, overheating, and cell imbalance. When charging lithium batteries, never exceed the recommended charge or discharge rates. Keep the battery temperature within the safe range. Use only healthy batteries with no signs of swelling or damage. Wear gloves and goggles when assembling or repairing a battery pack. Use insulated tools to prevent short circuits. Always insulate exposed wires and terminals with heat shrink tubing or tape.

A table of essential safety practices:

You should also monitor your battery pack during use. The BMS provides real-time data and can alert you to problems before they become dangerous. When charging lithium batteries, always stay nearby and check for heat or swelling. If you notice any unusual signs, stop using the battery and dispose of it safely. By following these tips, you can extend the life of your battery and keep your projects safe.

You can build a safe and reliable battery pack by following the right steps.

• Series connections raise battery voltage, while parallel connections increase battery capacity.
• Always use matched battery cells from the same batch and check each battery’s voltage before connecting.
• A Battery Management System protects your battery from overcharge, over-discharge, and short circuits.
• Use a strong battery enclosure and monitor battery temperature during charging.

Careful planning and double-checking every battery connection help you avoid battery failures and keep your battery pack safe for years.

常见问题

How do you know if your battery pack is safe to use?

You should check each battery for swelling, leaks, or damage. Use a multimeter to test voltage. Make sure your battery management system works. If you see any warning signs, stop using the battery right away.

Can you mix different brands of battery cells in one pack?

You should never mix different brands of battery cells. Each battery may have a different capacity or voltage. Mixing them can cause imbalance, overheating, or even fire. Always use the same type and brand for every battery in your pack.

What happens if you connect a battery with a different voltage?

If you connect a battery with a different voltage, you risk damaging the battery pack. The battery may overheat, leak, or even explode. Always match the voltage of every battery before you connect them together.

How do you store your battery pack safely?

Store your battery pack in a cool, dry place. Keep each battery away from metal objects. Do not store a battery in direct sunlight or near heat. Charge the battery to about 50% before long-term storage. Check the battery every few months.

Tip: Always label your battery pack with the date and type. This helps you track battery health and safety.