Battery chemistry & storage
Enter the continuous power output you need. See how much each battery chemistry would need to weigh to deliver it.
How it works
Step 1
Use the steady wattage you'd run for minutes or hours at a time, since that's what power density actually needs to cover, not a momentary startup spike. The C rate discharge calculator can help you total this up from individual appliances.
Step 2
The spread is often dramatic, especially for lead acid and flow batteries, which trade power density for other advantages.
Step 3
A chemistry with lower power density can still be the right call if weight isn't a constraint. The energy density comparison covers the related but different question of total stored energy.
Energy density asks how much total energy a battery can store per pound, while power density asks how fast that energy can come out. Two batteries can hold the same total energy but differ enormously in how much continuous current they can safely deliver, which is exactly why this comparison looks so different from the energy density comparison, a distinction NREL's energy storage research treats as two separate cell-design priorities rather than one combined metric.
NMC's higher typical continuous C-rate rating, combined with its higher energy density, compounds into meaningfully better power density than LFP. That's part of why NMC still shows up in applications with demanding power needs, like power tools, performance EVs, or a genuinely power-hungry household load such as the one covered in the battery size for well pump backup tool, even though LFP wins on cycle life and safety covered in the LFP vs NMC cycle life comparison.
Both chemistries are built around steady, moderate discharge rather than high continuous current, which shows up as a low sustainable C-rate on top of already-low energy density. That combination is why a modest power need can translate into an impractically heavy lead acid or flow battery bank, even when either chemistry might make sense for a lower-power application, a weight penalty that's especially unforgiving in a compact build with little room to spare, like the one covered in the tiny house battery sizing calculator.
If your power need is closer to a brief surge than a sustained draw, the C rate vs inverter output tool covers that separate scenario, and the fast charge capability comparison looks at the same power density question from the charging side. This weight-versus-power tradeoff is part of how the DOE's Office of Electricity evaluates storage hardware for high-power grid applications too.
Questions
Energy density measures how much total energy a battery stores relative to its weight or size, while power density measures how fast that energy can be delivered. A battery can have high energy density but low power density if its cells aren't built for high discharge current, which is common in lead acid and flow batteries.
NMC generally leads on power density among common storage chemistries, combining relatively high energy density with a higher sustainable C-rate than LFP. For a 3,000-watt continuous load, NMC needs roughly 20 pounds of battery, compared to about 39 pounds for LFP.
Lead acid combines low energy density with a low sustainable C-rate, typically well under 1C for deep-cycle types, which compounds into very poor power density. Delivering a modest 3,000-watt continuous load could require over 1,000 pounds of lead acid battery, versus under 40 pounds of LFP.
Yes, for a different reason than lead acid. Flow batteries are typically designed and sized for steady, moderate discharge over long periods rather than short bursts of high power, so their power density per unit of weight is among the lowest of common storage chemistries.