Why the old rules exist at all
Almost every handed-down battery rule of thumb dates from the era before lithium — from nickel-cadmium (NiCd) and nickel-metal-hydride (NiMH). These chemistries had real quirks that no longer apply to lithium. Anyone who transfers the old rules is optimising against a problem the cell doesn't even have, and causing a new one in the process.
From practice: mobile battery boxes at proLogistik
Since 2016 we have supplied proLogistik with mobile battery boxes in the Peli Case — several hundred units per year, designed for up to a week of runtime in order-picking operation. In the fleets the difference in charging behaviour is directly visible: boxes moved within the mid SoC window and not parked permanently full on the charger after the shift reach noticeably more cycles than identical boxes that are run empty and topped up to the brim every day. The hardware is identical — the difference is the charging habit.
The rules for operation
- Partial cycles instead of full cycles — 20–80 % SoC spares the cell.
- Avoid deep discharge — don't deliberately run it empty; the BMS is the last line of defence, not the strategy.
- Don't park permanently full — after the shift, don't leave it at 100 % on the charger for weeks.
- Storage: 50–60 % SoC, cool — not full, not empty.
- Protect from heat — temperature is the second major ageing driver alongside SoC.
Before the purchase, the one question no rule of thumb answers is decisive: which cell chemistry, which BMS and which construction fit the application? That is exactly where it is decided whether a battery becomes a wear part or a piece of operating equipment.
The five myths fact-checked
1 · The memory effect
„If I don't discharge fully, the battery will 'remember' a smaller capacity."
Fakt: The memory effect was a phenomenon of NiCd cells. In lithium-ion and LiFePO4 it does not exist. Partial discharges do no harm — they are in fact gentler than full cycles. So the rule is turned on its head.
2 · Fully empty first, then charge
„Before charging, the battery has to be completely discharged."
Fakt: Deep discharge is one of the strongest ageing drivers. If the cell voltage drops below the discharge cut-off voltage (roughly 2.5 V for LFP, around 3.0 V for Li-NMC), the cell begins to take damage; a good BMS switches off beforehand. Partial cycles in the mid-range (roughly 20–80 % SoC) deliver a multiple of the cycle count of a full 0–100 % cycle.
3 · Always store at 100 % and fully charged
„Full is best, for storage too."
Fakt: A high state of charge stresses the cell chemistry, and heat amplifies it. Calendar ageing rises with SoC and temperature — a cell stored at 100 % and warm loses considerably more capacity per year than one at a medium SoC in the cool. For storage: around 50–60 % SoC, cool. 100 % belongs in operation, not on the shelf.
4 · Lithium batteries explode easily
„A lithium battery is a bomb that can go off at any time."
Fakt: Thermal runaway occurs practically only under mishandling — mechanical damage, external short circuit or over-temperature from outside. Onset lies, depending on the chemistry, roughly between 150 °C (NMC) and 200–250 °C (LFP); LFP is considerably more stable because the cathode releases no oxygen on overheating. A correctly designed BMS with over-voltage, over-current and over-temperature protection keeps the cell within its safe window. The danger lies in mishandling, not in the chemistry itself.
5 · All lithium batteries are the same
„'Lithium' is 'lithium'."
Fakt: Three things decide how a pack behaves: cell chemistry (LFP: safe, long-cycle-life, lower energy density — Li-NMC: higher energy density, more sensitive), BMS (protection limits, balancing, diagnostics) and mechanical construction (cooling, interconnection, contacting). Two packs with the same cells can differ markedly in service life and safety if the BMS and construction do not fit.