September 10, 2026

Connecting 12.8V 100Ah batteries in series and parallel

You can connect two, three, or four BUKNUWO 12.8V 100Ah Bluetooth LiFePO4 batteries to build a bank for an RV, boat, solar or off-grid installation, or backup power system. The arrangement you choose depends on the voltage your equipment needs and how much capacity you want.

Before buying cables or making connections, check the manual for your exact model. Both the batteries and their BMS must support the number of batteries you plan to connect.

Choose the arrangement your equipment needs

Series wiring adds the battery voltages together and leaves the amp-hour capacity unchanged. Use it when your equipment needs a higher voltage: a 24V inverter normally needs a 24V-class bank, and a 48V inverter normally needs a 48V-class bank.

Parallel wiring keeps the bank at 12.8V and adds capacity for longer runtime. In an RV with a 12V electrical system, for example, you could expand a 100Ah bank to 200Ah, 300Ah, or 400Ah.

Check the voltage requirements of your inverter, MPPT solar charge controller, DC loads, and charging equipment before choosing either arrangement.

Configuration	Nominal voltage	Capacity	Nominal energy
One battery	12.8V	100Ah	1.28kWh
2S	25.6V	100Ah	2.56kWh
3S	38.4V	100Ah	3.84kWh
4S	51.2V	100Ah	5.12kWh
2P	12.8V	200Ah	2.56kWh
3P	12.8V	300Ah	3.84kWh
4P	12.8V	400Ah	5.12kWh

In the table, S means series and P means parallel. The same number of batteries stores approximately the same nominal energy in either arrangement.

Check the batteries before you start

1 Check compatibility

Choose batteries with the same chemistry, voltage, capacity, and model. Their age and condition should also be similar. Do not combine a 12.8V 100Ah battery with a 12.8V 200Ah battery unless the manufacturer approves it.

Check the series and parallel limits for your BUKNUWO model and its BMS against the product wiring diagram and user manual.

2 Disconnect equipment

Disconnect chargers, inverters, solar controllers, and loads before installing the bank or changing any battery connections.

3 Check each battery

Measure each battery with a multimeter. Before connecting them, bring them to a similar voltage and state of charge using the balancing procedure in the battery manual. This is especially important for parallel banks.

Do not directly connect batteries in parallel if their voltages differ significantly. The higher-voltage battery can immediately drive a large equalization current into the lower-voltage battery.

4 Check cables and protection

Use battery cables, terminals, fuses, circuit breakers, and busbars rated for the installation. Never let a tool or another conductive object bridge a battery's positive and negative terminals.

Keep current paths balanced in parallel banks

To help parallel batteries share current evenly, use cables with similar lengths, wire gauges, terminal sizes, and resistance.

For a larger bank, run the cables to dedicated positive and negative busbars. This avoids stacking many high-current cables on a single terminal and helps keep the wiring tidy and current paths balanced.

Connect batteries in series

Work from one battery to the next, connecting positive to negative. When you reach the end, the two unused terminals are the bank outputs. The examples below identify which terminal serves as system positive and which serves as system negative.

Use only an arrangement approved for your battery model. Keep charging sources and loads disconnected while wiring.

Two batteries in series 2S

With two batteries, you get 25.6V at 100Ah, or 2.56kWh of nominal energy. This is a 24V-class bank.

· Connect Battery 1 positive (+) to Battery 2 negative (-).

· Use Battery 1 negative (-) as system negative.

· Use Battery 2 positive (+) as system positive.

Three batteries in series 3S

A third battery brings the bank to 38.4V at 100Ah, with 3.84kWh of nominal energy. Make these connections:

· Connect Battery 1 positive (+) to Battery 2 negative (-).

· Connect Battery 2 positive (+) to Battery 3 negative (-).

· Use Battery 1 negative (-) as system negative and Battery 3 positive (+) as system positive.

Four batteries in series 4S

For a 48V-class system, use four batteries in series only if your model and BMS are approved for 4S operation. The bank has a nominal voltage of 51.2V, a capacity of 100Ah, and 5.12kWh of nominal energy.

· Connect Battery 1 positive (+) to Battery 2 negative (-).

· Connect Battery 2 positive (+) to Battery 3 negative (-).

· Connect Battery 3 positive (+) to Battery 4 negative (-).

· Use Battery 1 negative (-) as system negative and Battery 4 positive (+) as system positive.

Before connecting an inverter or charger, check polarity and measure the voltage across the completed bank with a multimeter.

Connect batteries in parallel

In a parallel bank, all positive terminals connect to the positive side and all negative terminals connect to the negative side. Voltage stays at 12.8V nominal as you add batteries.

Two batteries in parallel 2P

Two matching batteries give you 200Ah at 12.8V, doubling the capacity of a single battery. Nominal energy is 2.56kWh.

· Connect the two positive (+) terminals together.

· Connect the two negative (-) terminals together.

Three batteries in parallel 3P

For a 300Ah bank, connect three matching batteries as follows. The bank remains at 12.8V and stores 3.84kWh of nominal energy.

· Connect all three positive (+) terminals to the common positive side of the bank.

· Connect all three negative (-) terminals to the common negative side.

Four batteries in parallel 4P

Four matching batteries provide 400Ah at 12.8V, with 5.12kWh of nominal energy. Use the busbars as the common connection points:

· Connect the positive (+) terminals of Batteries 1, 2, 3, and 4 to the positive busbar.

· Connect the negative (-) terminals of Batteries 1, 2, 3, and 4 to the negative busbar.

Once the checks below are complete, connect your inverter, charger, MPPT controller, or DC load through the bank's main positive and negative outputs.

Before connecting equipment

Check polarity, then measure the completed bank voltage with a multimeter. Confirm that the inverter, charger, solar charge controller, and other equipment accept that voltage. Before switching on, also check the cable sizes and the BMS limits for your arrangement.

Choose a charger for a series bank

Choose the charger for the whole bank. If your battery specifications give a maximum charging voltage of approximately 14.6V per battery, the corresponding values for a series bank are:

Series bank	Example charging voltage
2S	Up to approximately 29.2V
3S	Up to approximately 43.8V
4S	Up to approximately 58.4V

Check the recommended charging voltage in the battery specifications before selecting a charger. A standard 14.6V single-battery charger must not be connected across an entire 24V, 36V-class, or 48V bank.

Using Bluetooth monitoring

Bluetooth lets you view supported battery data in an app. It does not change the wiring: a Bluetooth battery follows the same series and parallel principles as a compatible non-Bluetooth model.

← Back to Installation & How-To