Master Glossary and Formula Reference
Every formula, the LFP numbers worth memorising, the abbreviations that collide, and a glossary covering the whole series.
Battery Fundamentals · Part 6 — Safety, Standards and Field Work · Chapter 17 · 11 min read
The reference chapter. Every formula used across this series in one place, the LFP numbers worth committing to memory, the abbreviations that collide and cause real confusion, and a glossary covering everything the other sixteen chapters use.
Wh = Ah × V
The one that matters most
3.65 / 2.50 V
LFP charge / discharge cut-off
≤30 mV
Target cell delta at full
×2 per 10 °C
Ageing rule of thumb
17.1 — Formula cheat sheet
Energy and configuration
Energy
Wh = Ah × V
The only honest basis for comparison.
Pack voltage
V_pack = S × V_cell_nominal
Pack capacity
Ah_pack = P × Ah_cell
Pack energy
Wh_pack = S × P × V_cell × Ah_cell
Total cells
N = S × P
BMS channels
Channels = S
P-groups self-balance.
Current, resistance and heat
Current from C-rate
I (A) = C-rate × Capacity (Ah)
C-rate from current
C-rate = I (A) ÷ Capacity (Ah)
Charge time (approx)
t (h) = Ah ÷ I_charge × 1.1
The 1.1 covers the CV taper.
Voltage under load
V_load = OCV − (I × R_internal)
Explains most field complaints.
Internal resistance
DCIR = ΔV ÷ ΔI
State the pulse duration.
Heat generation
P_heat (W) = I² × R
Series resistance
R_total = R1 + R2 + …
Parallel resistance
R_total = R_cell ÷ P
State, health and range
Depth of discharge
DOD % = 100 − SOC %
Capacity SOH
SOH % = (Present capacity ÷ Rated capacity) × 100
Coulombic efficiency
CE % = (Ah_discharge ÷ Ah_charge) × 100
Round-trip efficiency
RTE % = (Wh_discharge ÷ Wh_charge) × 100
Usable energy
Wh_usable = Wh_pack × DOD limit × efficiency
Range estimate
km = Wh_usable ÷ Consumption (Wh/km)
Ageing rule of thumb
Rate ≈ ×2 per +10 °C
Arrhenius, close enough to design against.
17.2 — Quick reference numbers for LFP
Representative values. Always verify against the datasheet of the cell in front of you.
| Parameter | Value |
|---|---|
| Nominal cell voltage | 3.2 V |
| Charge cut-off | 3.65 V |
| Discharge cut-off | 2.50 V |
| Storage voltage (40–60 % SOC) | ~3.28–3.30 V |
| Balance start threshold (typical) | 3.40 V |
| Charge temperature range | 0 to 45 °C |
| Discharge temperature range | −20 to 60 °C |
| Storage temperature (ideal) | 0 to 35 °C |
| Target cell delta at full charge | ≤30 mV |
| Self-discharge | 2–3 % per month |
| Busbar joint resistance limit | ~50 µΩ |
| Typical e-rickshaw duty | 0.2–0.3C continuous, ~1C peak, 0.2–0.5C charge |
17.3 — Abbreviations that collide
Important
Four abbreviations carry two meanings each, and all four appear on real datasheets and BMS configuration screens. They are set out with worked disambiguations in Chapter 9. In summary:
| Abbreviation | Meaning A | Meaning B | Write instead |
|---|---|---|---|
| OCV | Open circuit voltage (a measurement) | Over charge voltage (a BMS threshold) | “OCV (open circuit)” and “OVP” |
| C | Capacity | Cathode; also C-rate | Q or “Cap”; spell out cathode; hyphenate C-rate |
| CC | Charge capacity | Constant current | Spell out “constant current” in charge profiles |
| RPT | Sometimes used loosely for cycle life | Reference Performance Test | CYC for cycle life; RPT only for the test |
And one category error rather than a collision: PTC is a protective device that acts on its own; NTC is a thermistor the BMS reads. They are frequently listed together as though they were the same class of component. One protects, one reports.
17.4 — Master glossary
17.4.1 — Chemistry
- LIB
- Lithium-ion battery
- LFP / LiFePO₄
- Lithium iron phosphate
- NMC / NCM
- Nickel manganese cobalt
- NCA
- Nickel cobalt aluminium
- LMO
- Lithium manganese oxide
- LCO
- Lithium cobalt oxide
- LTO
- Lithium titanate — an anode material, not a cathode
- Na-ion / SIB
- Sodium-ion battery
- SLA
- Sealed lead acid
- VRLA
- Valve-regulated lead acid
- AGM
- Absorbent glass mat
- NiMH
- Nickel metal hydride
- LiPF₆
- Lithium hexafluorophosphate — the usual electrolyte salt
- SSB
- Solid-state battery
17.4.2 — Form factor and construction
- CYL
- Cylindrical
- PRIS
- Prismatic
- PCH
- Pouch
- SEI
- Solid electrolyte interphase
- CID
- Current interrupt device — one-shot, pressure actuated
- PTC
- Positive temperature coefficient — a protective device
- NTC
- Negative temperature coefficient — a thermistor sensor
- CTP
- Cell-to-pack
- CTC
- Cell-to-chassis
- Busbar
- Conductive link between cells
- Module
- Sub-assembly of cells within a pack
- Pack
- Complete battery assembly
17.4.3 — Electrical
- Ah / mAh
- Ampere-hour / milliampere-hour — a charge count
- Wh / kWh
- Watt-hour / kilowatt-hour — energy
- Ω / mΩ / µΩ
- Ohm / milliohm / microhm
- OCV
- Open circuit voltage — rested, no load
- CCV
- Closed circuit voltage — under load
- EMF
- Electromotive force
- IR
- Internal resistance
- DCIR
- DC internal resistance — from a pulse, predicts sag
- ACIR
- AC internal resistance — 1 kHz, used for sorting
- EIS
- Electrochemical impedance spectroscopy
- C-rate
- Current as a multiple of rated capacity
- Shunt / Hall
- Current measurement methods — shunt for accuracy at low current, Hall for isolation
17.4.4 — State and performance
- SOC
- State of charge
- DOD
- Depth of discharge
- SOH
- State of health
- SOP / SOE
- State of power / state of energy
- BOL / EOL
- Beginning of life / end of life
- CE
- Coulombic efficiency — discharge Ah ÷ charge Ah
- RTE
- Round-trip efficiency — discharge Wh ÷ charge Wh
- CC / CV
- Constant current / constant voltage charge phases
- CAL
- Calendar life
- CYC
- Cycle life
- RPT
- Reference Performance Test
- K-value
- Self-discharge screening metric, in mV/day
17.4.5 — Protection and BMS
- BMS
- Battery management system
- OVP
- Over voltage protection
- UVP
- Under voltage protection
- OCP
- Over current protection
- SCP
- Short circuit protection
- OTP
- Over temperature protection
- UTP
- Under temperature protection — the one that prevents cold-charge plating
- RCP / RVP
- Reverse current / reverse voltage protection
- TCO
- Thermal cut off
- MOSFET
- The switching device that makes and breaks the pack circuit
- AFE
- Analog front end — the cell measurement IC
- VCU
- Vehicle control unit
- CAN / RS485 / BLE
- Communication buses
17.4.6 — Standards, quality and regulation
- UN 38.3
- Mandatory transport test standard
- UN 3480 / 3481
- Shipping classifications — cells alone / cells with equipment
- IEC 62133-2
- Portable sealed secondary lithium cell safety
- IEC 62619
- Industrial lithium batteries including stationary storage
- IS 16046
- Indian adoption of IEC 62133
- AIS 156
- India, L-category (2W/3W) — the operational standard here
- AIS 038 / AIS 048
- M and N category vehicles / older EV battery standard
- CMVR
- Central Motor Vehicles Rules
- ARAI / ICAT
- Indian testing and certification agencies
- BIS
- Bureau of Indian Standards
- UN ECE R100
- Electric powertrain safety (Europe)
- ISO 6469
- Electrically propelled road vehicle safety
- UL 2580 / UL 1973
- Battery safety — vehicles / stationary
- NFPA 855
- Energy storage installation safety
- RoHS / REACH
- Hazardous substance restriction / EU chemical registration
- BWMR 2022
- India’s Battery Waste Management Rules
- EPR / CPCB
- Extended producer responsibility / Central Pollution Control Board
- ISO 9001 / IATF 16949
- General / automotive quality management
- AQL
- Acceptable quality limit
- IP rating
- Ingress protection
- MSDS / SDS
- (Material) safety data sheet
17.4.7 — Manufacturing and testing
- EOL test
- End-of-line test
- Hi-pot
- Dielectric withstand test
- Megger
- Insulation resistance test
- Formation
- The first controlled cycles, where the SEI is built
- Degassing
- Venting and resealing after formation
- Calendering
- Pressing the coated foil to controlled density and porosity
- DFM
- Design for manufacture
- FMEA
- Failure mode and effects analysis
- PPAP
- Production part approval process
- RH
- Relative humidity — dry room control during electrolyte filling
17.5 — Where to go next
Three things are worth more than any further reading, in this order.
| Investment | What it gives you |
|---|---|
| A cell cycler | Characterise your own cells. The gap between the datasheet and reality is the most educational number you will ever measure, and it is specific to your supplier. |
| A milliohm meter and a thermal camera | Between them they diagnose most field failures, because most field failures are resistance problems. Cheaper than a handful of warranty replacements. |
| A bench log of every returned pack | Cell voltages, IR, fault codes, charger serial, and what it turned out to be. Within a year it is a failure-mode database specific to your product, your suppliers and your customers. |
For standards, obtain AIS 156 with amendments, IS 16046 / IEC 62133-2, the UN 38.3 test summary format, and the BWMR 2022 and CPCB EPR portal requirements. Those four are operational rather than academic for anyone selling batteries in India — see Chapter 14.
Chapter summary
- ✓Wh = Ah × V is the formula that prevents most bad comparisons. Convert everything to watt-hours first.
- ✓V_load = OCV − (I × R_internal) explains most field complaints, and P_heat = I² × R explains why they get worse.
- ✓For LFP: 3.2 V nominal, 3.65 V charge cut-off, 2.50 V discharge cut-off, balance from about 3.40 V, ≤30 mV delta at full charge, 0–45 °C to charge.
- ✓Four abbreviations carry two meanings each — OCV, C, CC and RPT. Disambiguate them in your own documentation rather than relying on context.
- ✓PTC protects on its own; NTC reports to the BMS. They are not the same class of component.
- ✓A cell cycler, a milliohm meter and a thermal camera are worth more than any amount of further reading.
- ✓A bench log of every return becomes a failure-mode database specific to your product within a year.
Frequently asked questions
What is the single most useful battery formula?+
Wh = Ah × V. Amp-hours count charge and are not comparable across chemistries, so converting everything to watt-hours before comparing is what prevents most bad purchase decisions. Two close seconds: V_load = OCV − (I × R_internal), which explains most field complaints, and P_heat = I² × R, which explains why they get worse.
What are the key voltage numbers for an LFP cell?+
3.2V nominal, 3.65V charge cut-off, 2.50V discharge cut-off, roughly 3.28 to 3.30V at a 40 to 60 per cent storage state of charge, and a typical balance start threshold around 3.40V. Charge temperature range 0 to 45°C, discharge −20 to 60°C, and a target cell delta at full charge of 30mV or less.
How do I calculate charge time?+
Approximately capacity in amp-hours divided by charge current, multiplied by 1.1 to cover the constant-voltage taper at the end. A 100Ah pack at 15A is about 7 hours; at 30A it is about 3.5 hours. The taper factor matters because the last 10 to 20 per cent of capacity arrives at steadily falling current.
Which abbreviations mean two different things?+
Four. OCV is open circuit voltage in measurement contexts and over charge voltage in some BMS documentation. C means capacity, cathode and C-rate. CC means charge capacity or constant current. RPT is sometimes used loosely for cycle life but properly means Reference Performance Test. Write “OCV (open circuit)” and “OVP”, use Q for capacity, spell out constant current, and use CYC for cycle life.
What equipment is worth buying to learn batteries properly?+
A cell cycler, to characterise your own cells — the gap between the datasheet and reality is the most educational number you will measure, and it is specific to your supplier. A milliohm meter and a thermal camera, which between them diagnose most field failures. And a bench log of every returned pack, which within a year becomes a failure-mode database specific to your product and customers.
Reviewed by
Battery Fundamentals is an original educational series on lithium battery technology. Threshold tables, cycle-life curves and worked examples use representative values drawn from published product specifications and widely-observed industry patterns, not measured data from a specific product. Always consult the current manufacturer datasheet before making design, purchasing, warranty or certification decisions.