Enter two batteries' current prices and specs from their listings.
Cost per usable Wh = price ÷ (Ah × 12.8 V × usable %). Lifetime cost divides that by rated cycles (makers usually rate cycles to 80% remaining capacity, under specific conditions). One 200 Ah battery is often cheaper per Wh and uses less wiring than two 100 Ah, but two 100 Ah batteries give redundancy and more combined BMS current (often 2 × 100 A vs 1 × 100–200 A). Also compare BMS continuous amps, low-temperature charge protection, Bluetooth monitoring, and warranty.
Safety: These are general estimates, not a design. Follow your equipment manufacturer's instructions and local electrical code, and consult a qualified electrician for anything connected to shore power, a house, or high-current batteries.
Usually cheaper per Wh and simpler to wire; two 100 Ah give redundancy and may allow more total current. Check each battery's BMS rating.
You can use ~90% of LiFePO4 vs ~50% of AGM, with thousands of cycles vs hundreds, so lifetime cost per kWh is usually much lower despite the higher price.
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