To connect 6 12-volt batteries in series and parallel to create a 24V system, you must use a 2-Series, 3-Parallel (2S3P) configuration. This means you first wire pairs of batteries in series to create three separate 24V strings, and then wire those three strings in parallel to multiply the amp-hour (Ah) capacity while maintaining the 24V nominal output. Assuming you are using standard 12V 100Ah batteries, this 2S3P bank will yield a nominal 24V output at 300Ah (7.68 kWh of total energy storage).

This guide traces the exact node-by-node path from the battery terminals to the load, maps the physical hardware to standard schematic symbols, and provides the exact multimeter thresholds you need to verify the bank before energizing your inverter.

Terminal Mapping and Diagram Symbol Key

Before cutting any wire, you must identify the physical terminals on your specific battery chemistry. Modern 12V LiFePO4 batteries (like the Ampere Time or SOK 12V 100Ah models) typically use M8 threaded stainless steel studs. Traditional flooded lead-acid or AGM batteries (like the Trojan T-1275 or VMAXTANKS) often use LPT (Large Post Terminal) lead posts with a 3/8-inch hole. The wiring diagram symbols remain the same regardless of the physical terminal type, but your crimp lugs and torque specs will change.

In standard DC schematics, a battery is represented by a pair of parallel lines (one long for positive, one short for negative). A busbar is drawn as a thick horizontal line intersecting multiple vertical drop lines. The load (inverter or charge controller) is shown as a circle with a loop or a specific manufacturer symbol.

Hardware Assumption: The table below assumes you are using M8 terminal LiFePO4 batteries and copper busbars. If using LPT lead posts, swap the M8 lugs for 3/8-inch ring terminals and reduce torque to 7-9 Nm to avoid stripping the soft lead.
2S3P Terminal Mapping and Interconnect Specifications
Node / Connection Point Physical Terminal Diagram Symbol Wire / Busbar Spec Torque Spec
Series Interconnect (B1+ to B2-) M8 Threaded Stud Short dashed line between cells 2/0 AWG Copper, 2-inch 10 - 12 Nm
String to Pos Busbar M8 Stud to 3/8" Busbar Hole Vertical line to thick horizontal 2/0 AWG Copper, 12-inch 10 - 12 Nm
String to Neg Busbar M8 Stud to 3/8" Busbar Hole Vertical line to thick horizontal 2/0 AWG Copper, 12-inch 10 - 12 Nm
Main Bank to Inverter Busbar to Inverter Lug Heavy line to load circle 2/0 AWG or 4/0 AWG Flex 15 Nm (Inverter side)
DC Ground Bond Neg Busbar to Chassis Three descending horizontal lines 6 AWG Bare or Green 5 Nm

Node-by-Node Wiring Trace (Source to Load)

For a balanced 2S3P bank, we use the busbar method rather than diagonal daisy-chaining. Diagonal wiring causes the first and last batteries in the parallel chain to carry disproportionate current, leading to premature degradation. Busbars ensure equal resistance for all three strings. According to Battery Stuff wiring guidelines, keeping interconnect lengths identical is critical for parallel balancing.

  1. Build String 1 (Nodes B1 & B2): Place Battery 1 (B1) and Battery 2 (B2) side-by-side. Connect the positive terminal of B1 to the negative terminal of B2 using a short 2/0 AWG series interconnect cable. B1 Negative is now the String 1 Negative node. B2 Positive is the String 1 Positive node.
  2. Build String 2 (Nodes B3 & B4): Repeat the exact process. Connect B3 Positive to B4 Negative. B3 Negative is String 2 Negative; B4 Positive is String 2 Positive.
  3. Build String 3 (Nodes B5 & B6): Connect B5 Positive to B6 Negative. B5 Negative is String 3 Negative; B6 Positive is String 3 Positive.
  4. Connect to the Negative Busbar: Mount a copper negative busbar (minimum 1/4" thick, 4-hole). Run identically sized 2/0 AWG cables from B1 Negative, B3 Negative, and B5 Negative to the three input holes on the negative busbar. Torque to 11 Nm.
  5. Connect to the Positive Busbar: Mount a copper positive busbar. Run identically sized 2/0 AWG cables from B2 Positive, B4 Positive, and B6 Positive to the positive busbar. Torque to 11 Nm.
  6. Main Load Path (Source to Inverter): Connect a heavy-duty 2/0 AWG or 4/0 AWG red cable from the main output stud of the Positive Busbar to the positive DC input of your 24V inverter. Install a Class-T fuse (e.g., 250A for a 5000W inverter) on this positive line within 7 inches of the busbar.
  7. Polarity and DC Ground Path: Connect a heavy-duty black cable from the main output stud of the Negative Busbar to the negative DC input of the inverter. Critical Ground Step: Run a dedicated 6 AWG green or bare copper wire from a grounding lug on the Negative Busbar directly to the system chassis ground and the inverter's dedicated earth ground terminal. This establishes the equipotential bonding path required to clear DC faults and prevent chassis shock.

Verifying the Bank with a Multimeter

Never connect the main inverter cables until you have verified the internal nodes with a digital multimeter (DMM). Set your DMM to DC Voltage (200V range) and use the following diagnostic trace.

  • Check Individual Cells: Place the red probe on B1+ and black on B1-. You must read between 12.8V and 13.4V (for LiFePO4) or 12.4V to 12.7V (for Lead-Acid). Repeat for all 6 batteries. If any cell reads below 11.5V, charge it individually before integrating it into the bank.
  • Check Series Strings: Move the black probe to B1- and the red probe to B2+. You should read exactly double the single cell voltage (e.g., 25.6V to 26.8V for LiFePO4). If you read near 0V, your series interconnect is backward or loose. If you read 12V, one battery is reversed.
  • Check Parallel Busbars: Place the black probe on the Negative Busbar main stud and the red probe on the Positive Busbar main stud. The reading must match your series string voltage (e.g., ~25.6V). If the voltage fluctuates or reads lower, you have a high-resistance connection on one of the parallel legs.
  • Verify Ground Continuity: Turn the DMM to the Resistance/Continuity setting (Ω). Place one probe on the Negative Busbar and the other on the bare metal chassis of your battery box or RV frame. The meter should read less than 0.5 ohms, confirming a solid DC ground bond.
DC Arc Flash Hazard: A 24V 300Ah bank can deliver over 3,000 amps in a dead short. Always wear safety glasses and insulated gloves when making the final busbar connections. Ensure your main Class-T fuse is installed on the positive line before you connect the final negative cable to the inverter.

Parallel Balancing and Edge Cases

The most common failure mode in a 6-battery 2S3P bank is parallel string imbalance. If the cables connecting the batteries to the busbars are even a few inches different in length, the resistance changes. According to Victron Energy's Wiring Unlimited guidelines, current takes the path of least resistance. The string with the shortest cables will deliver the most current during high-load inverter draws, causing those specific batteries to heat up, experience deeper voltage sag, and trigger their internal BMS low-voltage disconnect prematurely.

To prevent this, cut all three positive parallel runs to the exact same physical length, and do the same for the three negative runs. Do not coil excess wire to make them fit; measure twice and cut once.

Another edge case involves mixing battery ages. Never add three brand-new 12V batteries to three older 12V batteries in a 2S3P configuration. The older batteries will have higher internal resistance, forcing the new batteries to do all the heavy lifting during discharge, and accepting all the bulk current during the absorption phase of solar charging. For a 6-battery bank, all units must be the same brand, same Ah rating, and purchased in the same batch to ensure matched internal impedance.