Understanding your efficiency comparison
What round trip efficiency actually bundles together
Round trip efficiency combines internal resistance losses during charge and discharge, BMS standby draw, cell balancing overhead, and, for some chemistries, additional parasitic loads like pumps. Rather than tracking each separately, this single percentage gives a practical shortcut for estimating total energy waste over a year of use, a figure worth folding into the savings with battery vs without battery tool for a complete picture of what a system actually saves you after these losses.
Why lithium chemistries dominate on efficiency
LFP and NMC both convert charge and discharge energy with minimal loss, typically landing in the 95% to 97% range, thanks to low internal resistance and minimal parasitic overhead, figures consistent with the efficiency benchmarks NREL's energy storage research publishes across storage chemistries. That efficiency advantage compounds daily over a system's life, adding up to real savings beyond just the purchase price covered in the lithium vs lead acid comparison.
Why lead acid and flow batteries lose more energy
Lead acid loses energy to gassing during charging, where some input energy breaks down water instead of storing charge, while flow batteries draw ongoing power to run circulation pumps regardless of how much net energy is being stored or released. Both effects are structural to how each chemistry works, not a sign of a poorly built product. See the flow battery vs lithium comparison for how that efficiency gap fits into the bigger cost picture, and the battery cost per kWh comparison tool for how a lower sticker price can still lose ground once efficiency losses are factored in.
What to check next
If a specific chemistry's efficiency loss looks concerning, the cell balancing loss calculator and internal resistance tool linked above can help pinpoint which part of that loss you might actually be able to reduce. This same efficiency accounting shows up in how the DOE's Office of Electricity evaluates real-world round trip efficiency for grid-scale storage deployments.