A lithium-ion battery is a black box you charge and discharge, and it never gives back exactly what you put in: its round-trip efficiency — energy out over energy in — falls short of 100% because current pushed through its internal resistance on both legs becomes heat, not stored or delivered energy. Charge faster and you raise the C-rate, and because resistive heating scales with current squared, a fast charge wastes far more energy as heat than a gentle one. Hold it fully charged and self-discharge quietly bleeds a little energy away even while idle. And every cycle nudges its usable capacity down — a fade that runs faster the deeper, faster, and hotter you cycle it — until it reaches the 80% end-of-life threshold. Set the capacity, charge rate, discharge load, hold time, resistance quality, and ambient temperature, then watch state of charge, power, temperature, and cycle-life fade play out live. It all runs on your device.
You are in the Physics lab.
Energy in during charging, energy out during discharge — and where the rest goes.
What the schematic, the energy-split bar and the two plots are telling you — then what repeated cycles do to the battery.
Energy from the grid flows in during charging, some of it is lost as heat, the rest is stored, and on discharge it flows back out through another loss before reaching the load. The gauge beside the schematic tracks live power against the battery's rated power, positive while charging and negative while discharging.
The energy-split bar breaks the round trip into three slices: the charge loss and discharge loss that both leave as resistive heat, and what's left as energy actually delivered to the load. Round-trip efficiency is delivered energy divided by energy in — the higher the C-rate or the weaker the resistance quality, the smaller that delivered slice gets.
The state-of-charge plot tracks percent charge through the charge, hold and discharge phases of one cycle, including the slow bleed of self-discharge during the hold. Run more cycles and the fade plot tracks usable capacity declining toward the 80% end-of-life threshold — faster the deeper, faster, and hotter each cycle runs, reported live as cycles to 80% and peak temp.
A resistive loss on every amp that flows, a self-discharge that never sleeps, and a cycle-life fade that plays out over hundreds of cycles, not minutes.
Any current flowing through the battery's internal resistance dissipates power as heat equal to current squared times resistance, on both the charge and discharge legs. Round-trip efficiency is energy delivered divided by energy in, and it drops whenever the C-rate (current relative to capacity) rises or the resistance quality is worse — a fast, high-current cycle wastes far more of the round trip as heat than a gentle one, even though it moves the same amount of charge.
Even with no charger and no load connected, a lithium-ion battery slowly loses charge to internal leakage current — self-discharge. It's usually a small fraction per day, but over a long hold time between charging and discharging, it measurably lowers the state of charge the battery starts its discharge from, on top of any resistive loss already paid during charging.
Every charge-discharge cycle leaves the battery's usable capacity a little lower than before, a decline tracked here as cycles to 80% — the count until capacity fades to 80% of its original value, a common end-of-life threshold. That fade runs faster with a deeper swing in state of charge per cycle, a higher charge or discharge C-rate, and higher ambient temperature, all stacked together in the peak temp the battery reaches during the run.