Turn off all loads and chargers
Verify all batteries are the same voltage and chemistry
Use batteries with similar capacity and age when possible
Fully charge each battery before connecting
Check each battery for damage, swelling, leaks, or corrosion
Clean the terminals before making connections
Connect all positive terminals together
Connect all negative terminals together
Use cables of equal length and proper gauge
Add a fuse or breaker on each battery’s positive lead if required
Tighten all connections securely
Measure the combined voltage after connecting
Confirm the system voltage matches one battery’s voltage
Connect the load or charger to the parallel battery bank
Recheck connections for heat, looseness, or abnormal voltage drop