Understanding your parallel configuration
What changes and what stays the same
Wiring batteries in parallel keeps voltage identical to a single unit while capacity and maximum current both scale directly with the number of units combined. This is the wiring approach to reach for when you need more energy storage or more available current at a voltage your equipment already expects, a common need in marine electrical systems where the marine battery bank sizing calculator covers this same scaling question for a boat's house bank.
Why identical units matter more here than you might expect
Mismatched voltage or internal resistance between parallel units can cause current to flow unevenly between them, with the lower-resistance unit picking up more than its fair share of load and wearing out faster as a result. Using the same model, ideally similar in age, is the simplest way to avoid this, and it's also why parallel-string behavior is part of what the UL 9540A test method examines, since uneven current sharing can create localized hot spots under fault conditions.
How parallel compares to series wiring
Parallel and series wiring solve different problems: parallel raises capacity and current at a fixed voltage, while series raises voltage while keeping capacity the same as a single unit. Many multi-battery systems actually use a combination of both, covered in the series-parallel mixed configuration tool, and the same series-versus-parallel tradeoff shows up on the panel side of a system too, worth comparing against the string sizing tool if you're planning the array alongside the battery bank.
What to check next
If you're unsure whether your target system voltage is the right one to begin with, the bank voltage selection tool can help work through that decision before you finalize a wiring plan. NREL's energy storage research covers the underlying current-sharing behavior in more technical depth if you want to go further into the electrochemistry behind it.