Short explanations of the terms used in the calculators: what each one means and where to find the value.
An amp-hour describes the electric charge a battery can deliver under specified conditions. A 100 Ah battery is not guaranteed to supply 100 A for one hour: the actual result also depends on chemistry, temperature, age and discharge current.
Used in: Charge time · Capacity & runtime · Series & parallel
A watt-hour is a unit of energy. Approximate battery energy is voltage in volts multiplied by capacity in Ah; 12 V × 100 Ah gives a nominal 1200 Wh.
Used in: Capacity & runtime · Series & parallel
C-rate compares charge or discharge current with battery capacity. For a 100 Ah battery, 0.1C means 10 A and 1C means 100 A; always check allowed values in the manufacturer’s documentation.
Used in: Charge time · Capacity & runtime
SoC indicates how much usable capacity remains in a battery. 100% means fully charged according to the chosen method, and voltage alone is not always enough to determine SoC reliably.
Used in: Charge time
DoD indicates how much capacity has been used since full charge. In a simple model, 80% SoC corresponds to 20% DoD, but system design should use the battery manufacturer’s limits.
Used in: Capacity & runtime
Nominal voltage is a conventional value used to describe a battery or system, such as 12 V. Actual voltage changes during charging and discharging and may differ noticeably from the nominal value.
Used in: Charge time · Capacity & runtime · Series & parallel · Voltage drop
Resting voltage is measured after charging and loads have been disconnected and the battery has had time to stabilise. Voltage measured under load or immediately after charging is not resting voltage.
Used in: Charge time
Charge efficiency indicates how much of the charge supplied by the charger is stored usefully. The remainder is lost, so a time estimate including efficiency is longer than the simple Ah ÷ A result.
Used in: Charge time
Absorption is a final charging stage for many lead-acid batteries, during which the charger holds a specified voltage while current gradually decreases. Its duration depends on the battery, charger, temperature and settings, so there is no universal value for every installation.
Used in: Charge time
A battery bank is a group of batteries connected to obtain the required voltage, capacity or both. Treat the bank as one complete system; voltage and Ah are not added in the same way for every connection type.
Used in: Charge time · Capacity & runtime · Series & parallel
A series string consists of batteries connected from the positive terminal of one to the negative terminal of the next. Voltages add together, while Ah capacity remains the same as for one battery.
Used in: Series & parallel
Continuous current is the value a battery, BMS, cable or device can carry for an extended period under specified conditions. Do not confuse it with short surge current; the lowest limit of any system component applies.
Used in: Series & parallel · Voltage drop
Peak current is a higher current drawn briefly, for example when a motor starts or an inverter powers up. The amp value alone is not enough; documentation must also state how long that current is permitted.
Used in: Capacity & runtime · Series & parallel · Voltage drop
A BMS monitors values such as cell voltage, current and temperature and may disconnect charging or loads when limits are exceeded. Its limits can be lower than those of the cells themselves, so consult the complete battery documentation.
Used in: Charge time · Capacity & runtime · Series & parallel
AGM is a sealed lead-acid battery in which the electrolyte is absorbed in a glass-fibre mat. It requires a charging profile suitable for the specific model; the AGM label does not define one universal voltage or current.
Used in: Charge time
A gel battery is a sealed lead-acid battery with electrolyte thickened into a gel. It is not the same as AGM and must be charged using the manufacturer’s specified voltages and limits.
Used in: Charge time
LiFePO4 is lithium iron phosphate chemistry used in traction batteries and energy storage. It requires a compatible charger and BMS, and its state of charge should not generally be inferred from voltage alone.
Used in: Charge time · Capacity & runtime · Series & parallel
VRLA means a valve-regulated sealed lead-acid battery. AGM and gel are VRLA types, but their construction differs and they may require different charging settings.
Used in: Charge time
Voltage drop is the difference between voltage at the start of a cable and voltage reaching the load while current flows. It increases with factors such as current and cable length and decreases with a larger conductor area.
Used in: Voltage drop
Resistivity is a material property describing resistance independently of a particular cable length and area. It depends on material and temperature, so a custom value must come from reliable data for the relevant conditions.
Used in: Voltage drop
Cross-section is the area of the cable’s metal conductor, not its diameter or insulated size. A larger area usually reduces voltage drop and heating, but protection and current-carrying capacity require separate checks.
Used in: Voltage drop
Loop length covers the complete current path from source to load and back. If the form asks for one-way distance, the calculator doubles it, so do not double it again.
Used in: Voltage drop
Self-consumption is power used by an inverter, UPS or other intermediate device independently of the connected load. Even a small value can noticeably reduce runtime at low loads.
Used in: Capacity & runtime
A sizing factor increases calculated capacity to allow for uncertainty, ageing or harsher conditions. A value of 1 adds no reserve, while 1.25 increases the required result by 25%; it is not a universal standard.
Used in: Capacity & runtime