Your 10 kWh Battery Isn't 10 kWh — Here's Why

Most solar battery buyers compare one number: kWh on the label. But that number doesn't tell you how much energy you can actually use, or how long the battery will keep delivering it. This video breaks down the two specs that really decide your backup time and your long-term cost — depth of discharge (DoD) and cycle life. Depth of discharge is the share of stored energy you can safely pull out before recharging. A 10 kWh battery rated at 90% DoD gives you around 9 kWh of usable energy. That held-back kWh isn't wasted — it's the buffer that protects the cells from deep-discharge stress and early capacity loss. LiFePO4 typically runs at 80–100% DoD, standard Li-ion (NMC/NCA) at 80–90%, and lead-acid at just 50–70%. That's why two batteries with identical nameplate capacity can power your home for very different lengths of time. Cycle life is the second half of the story. One cycle equals energy use adding up to 100% of capacity — so two half-discharges count as one full cycle. LiFePO4 commonly delivers 3,000–7,000 cycles, Li-ion 2,000–4,000, and AGM lead-acid as few as 500–1,000. If your system cycles daily (roughly 300–365 times a year), cycle life becomes the single most important spec you can look at. If you only need backup during occasional outages, a cheaper chemistry may be perfectly fine. We also cover the quick backup-time formula — capacity × DoD ÷ load = hours — plus the real-world losses that shorten it: inverter efficiency, round-trip efficiency, temperature, and age. And we explain why cost per cycle ($0.05–$0.15/kWh for LiFePO4 vs $0.10–$0.30 for lead-acid) is a far better comparison than sticker price alone. Match the battery to how you'll actually use it — not to the number on the label.

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