Understanding your series configuration
What changes and what stays the same
Wiring batteries in series adds voltage while keeping maximum current the same as a single unit, since the same current flows through the whole string in sequence. Total energy still increases because energy equals voltage times amp-hours, so even though amp-hour capacity doesn't change, higher voltage means more total kWh. If you haven't settled on a target voltage yet, the off-grid battery bank voltage selection tool is a good place to work that out first.
Why the weakest unit sets the ceiling in series
Unlike parallel wiring where currents from each unit add together, a series string can only push as much current as its weakest unit safely allows, since every battery in the string carries the exact same current. A single undersized or degraded unit in an otherwise strong series string limits the whole string's performance, and uneven behavior within a string is part of what the UL 9540A test method looks at when evaluating fault conditions across a battery system.
Why higher voltage is often the goal
Raising system voltage lowers current for the same power output, which reduces voltage sag and resistive losses covered in the voltage sag under load calculator, and it's frequently required to match a specific inverter's input voltage window, worth checking directly against the MPPT voltage window calculator. This is why many larger systems settle on 48V or higher rather than staying at 12V or 24V.
What to check next
If you're not sure whether series, parallel, or a combination fits your project best, the bank voltage selection tool is a good starting point before committing to a specific wiring plan. NREL's energy storage research covers the underlying current behavior in series strings in more technical depth if you want to go further into the electrochemistry behind it.