Battery Interconnect Cable Sizer
Sizes short, heavy-gauge battery jumper cables between series or parallel battery cells to maintain sub-milliohm balance and prevent cell drift. For main battery bank to inverter cables, use the Inverter Cable Sizer.
Enter the values above and click Calculate to view recommendations and engineering specifications.
Critical Battery Bank Balancing Rules
Calculation Assumptions
- Equalized resistance across all parallel paths to prevent cell current imbalance.
- Short cable lengths (<18 inches) where ampacity and physical terminal torque dominate over voltage drop.
Engineering Limitations
- Does not calculate cell internal resistance variance; requires matched battery ages and cable lengths.
Two 100Ah LiFePO4 batteries paralleled to feed a 2000W inverter require 2/0 AWG (67.4 mm²) interconnect links with equal lengths to avoid pulling 70% of the current through the nearest battery.
Because battery interconnects are very short (usually 6 to 12 inches), thermal ampacity and micro-ohm resistance matching are the governing factors rather than percentage voltage drop:
- Equal Length Cables: All parallel interconnect cables must be cut to the exact same millimeter length and crimped identically. Unequal wire lengths produce different branch resistance, causing the shorter wire to supply more current and cycle the connected battery faster.
- Diagonal Load Connection: When drawing power from a parallel battery bank, never connect both main positive and negative inverter cables to the same battery. Connect the main positive to Battery #1 and the main negative to Battery #N (the opposite end of the bank). This forces current to traverse an equal number of interconnect jumpers through every battery.
Frequently Asked Questions
What size wire should battery interconnect jumpers be?
Battery interconnect jumpers must be sized to carry the entire continuous current of the battery bank's largest load (typically the inverter at low-voltage cutoff plus 125% safety factor). In systems with a 2000W-3000W 12V inverter, interconnect cables must be at least 2/0 AWG or 4/0 AWG pure copper with 105°C marine-rated insulation.
Why must parallel battery interconnect cables be identical in length?
In parallel battery banks, uneven cable lengths create unbalanced electrical resistance. The battery with shorter cables will supply more current during discharge and take more current during recharge, leading to thermal degradation, premature cell wear, and chronic state-of-charge mismatch between paralleled batteries.
What is diagonal cross-corner wiring on a parallel battery bank?
Diagonal cross-corner connection connects the main system positive cable to the first battery in the bank and the main system negative cable to the last battery in the bank. This ensures that current flowing through every individual battery encounters an identical total circuit conductor length and internal resistance.
Should I use solid copper busbars or flexible cables for interconnects?
Solid nickel-plated copper busbars offer the lowest possible resistance and cleanest terminal layout for modular lithium cells (such as prismatic LiFePO4 cells). However, in mobile RV and marine installations subject to vibration, flexible Class K or Class M ultra-flexible stranding with heavy-duty tinned copper crimp lugs is preferred to prevent mechanical stress on terminal posts.