The correct way of connecting a multiple parallel battery bank is indicated in below drawings. Use a positive and negative post, connect diagonally or use busbars. The main aim is to make sure the total path of the current into each battery is equal.
3.4 Battery bank balancing
Multiple 12V batteries can be connected in series to create a higher voltage like 24V or 48V. Only batteries are not completely identical and have minute differences in internal resistance. When a series string of batteries is charged you can end up with a variance in terminal voltages on each battery. This will cause the batteries to become unbalanced over time, and one of the batteries in a string will fail prematurely.
To check if cell unbalance is happening in your system: • Charge the battery bank. • Measure at the beginning of the bulk charge stage. This is when the charger is charging at full current. • Measure the individual battery voltages of one battery. • Measure the individual battery voltages of the other battery. • Compare the voltages. • If there is a noticeable difference between these voltages, then the battery bank is unbalanced.
To prevent initial battery unbalance you will need to fully charge each individual battery prior to connecting them in series (and/or parallel). to prevent unbalance in the future as the batteries are aging use a Battery balancer.
The battery balancer balances measures, warns and corrects battery imbalance. When a 24V battery bank is charged, and the voltage has reached 27V, the Battery Balancer will turn on. It will compare the voltage of both batteries and if it detects that the voltage of one battery is higher than the other battery it will draw a current of up to 1 A from the battery until the voltages are the same again. For a 24V system a single battery balancer is needed. And for a 48V system 3 battery balancers are needed, one between each two batteries. For more info see: https://www.victronenergy.com.au/batteries/battery-balancer
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