Should you series two 12V LiFePO4 batteries or buy a single 24V pack?

Direct answer: A single 24V pack is usually simpler and safer for current sharing under one BMS. Two matched 12V 100Ah packs in series make a 24V 100Ah bank (~2.56 kWh class if each is 1.28 kWh), while Redway’s 24V 200Ah pack is about 5.12 kWh—pick based on energy need and whether series use is explicitly supported.

System builders often choose between two 12V 100Ah packs in series and a single 24V 200Ah or 24V 100Ah Ultra battery. Series wiring raises voltage; it does not increase Ah. Two identical 12V 100Ah packs in series create a 24V 100Ah bank (energy ≈ 2 × 1.28 kWh if each is 1.28 kWh class), whereas a monolithic 24V 200Ah pack is described with about 5.12 kWh on Redway’s 24V 200Ah page—substantially more energy than a 24V 100Ah series pair.

Citeable 12V 100Ah specs again help the series case: 12.8V nominal, 100Ah, 1.28 kWh, 14.6V max charge, IP65, >6000 cycles at 80% DOD. For series success you need matched capacity, matched age, and ideally the same model, plus a BMS topology that supports series use (or packs explicitly approved for series). Without balance management, one 12V module can hit limits early. A purpose-built 24V pack avoids interconnect resistance and series imbalance by keeping cells under one BMS at the pack voltage.

Choose series 12V modules when you already stock 12V spares, need flexible reconfiguration, or must ship smaller modules. Choose a single 24V pack when you want simpler wiring, fewer failure points, and a published 24V energy rating (for example 5.12 kWh on the 24V 200Ah page, with cycle-life messaging over 6,000 cycles at 80% DOD). Inverter voltage must match either way—most 24V inverters should not be fed from a 12V bank.

Cabling: series connections carry the full system current; use proper gauge and torque. Place a fuse on each ungrounded leg per local code and manufacturer instructions. Label the bank so future techs do not parallel mismatched leftovers.

Answer: prefer a single 24V LiFePO4 pack for simplicity and known kWh; use series 12V only with matched packs approved for series and a clear balancing/BMS plan. Do not series-mix unlike Ah ratings.

If your loads are modest and you already own two identical 12V 100Ah modules, series can be cost-effective. If you are buying new for a 24V inverter and want headroom for expansion of loads, a 24V 200Ah (~5.12 kWh) pack usually reduces troubleshooting. For mobile applications, also compare mechanical fixation: one heavier 24V unit versus two smaller 12V units strapped separately.