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Forklift Traction Battery Guide

Traction battery basics for forklifts: 2 V cells and system voltage, C5 capacity, PzS/PzB/PzV cells, tray size and counterweight, REMA and SB connectors, charging, and what to send in an RFQ.

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A forklift traction battery is not a larger starter battery. It is an assembly of individual cells in a steel tray, sized to a specific truck's battery compartment, weight range and voltage, and it is typically discharged and recharged every shift. Quoting one correctly depends on data that is rarely printed on a single label. This guide covers the technical basics and the information needed for an accurate request.

Cells, voltage and capacity

2 V cells in series

A lead-acid traction battery is built from 2 V cells connected in series. EnerSys gives the nominal voltage of its traction batteries simply as 2.0 V multiplied by the number of cells. The system voltage therefore fixes the cell count:

System voltage Number of 2 V cells
24 V 12
36 V 18
48 V 24
72 V 36
80 V 40

The truck's data plate states the battery voltage it requires. A battery of the wrong voltage is not a substitute, regardless of capacity.

Capacity at the 5-hour rate (C5)

Traction battery capacity is rated at the 5-hour rate, not the 20-hour rate used for starter batteries. IEC 60254-1 (published in India as the identical IS 5154-1) defines nominal capacity for a discharge time of 5 hours at a cell temperature of 30 °C to a cut-off voltage of 1.70 V per cell. A 48 V 700 Ah battery is therefore 24 cells, each rated 700 Ah at the 5-hour rate. Do not compare a traction battery's C5 figure with a C20 or C10 figure for another battery type; see the deep cycle battery guide for how rates change capacity.

Cell types: PzS, PzB and PzV

European traction cells are identified by designations such as 5 PzS 700:

  • The leading number is the number of positive plates. Jungheinrich's operating instructions describe cells with two to ten (or twelve) positive plates, with the type designation built from the plate count and capacity.
  • The final number is the nominal C5 capacity in Ah. EnerSys lists 5 PzS 700 as a 700 Ah (5-hour) cell.
  • The letters identify the cell family:
Designation Construction Dimension series (per EnerSys)
PzS Tubular positive plates, flooded electrolyte DIN/EN 60254-2 and IEC 254-2 series L
PzB Tubular positive plates, flooded electrolyte IEC 254-2 series E
PzV Tubular plates with immobilised (gel) electrolyte, valve-regulated Manufacturer data

PzS and PzB cells with the same capacity are not dimensionally interchangeable, because they follow different dimension series. The cell type must match the tray and the compartment.

Within a cell series, capacity scales with plate count. In EnerSys's Perfect Plus range, for example, 2 PzS 120 to 10 PzS 600 cells share the same width and height and grow in length with each added plate, while cells such as 5 PzS 700 are taller.

Tray dimensions and counterweight

The cells sit in a steel tray that must fit the truck's battery compartment. On counterbalance forklifts the battery is also part of the counterweight that keeps the truck stable under load.

  • Jungheinrich's data plate lists the minimum and maximum battery weight alongside the battery voltage, and its manual states that the weight and dimensions of the battery have a considerable effect on the operational safety of the truck, and that battery equipment may only be replaced with the manufacturer's agreement.
  • Toyota Material Handling notes that using a battery that meets the truck's minimum battery weight requirement is crucial to safe operation, and that some truck data plates show the battery compartment width.
  • In the United States, OSHA's powered industrial truck rule (29 CFR 1910.178) requires the manufacturer's prior written approval for modifications affecting capacity and safe operation, and prohibits additional counterweighting unless approved by the truck manufacturer.

A lighter battery chemistry, such as lithium-ion, therefore has to be ballasted or built to meet the truck's weight range. Toyota describes its lithium-ion forklift batteries as having built-in counterweight to meet minimum and maximum truck weight requirements.

Connectors

The battery connects to the truck and charger through a plug-and-socket connector. Two families are widely used:

REMA (DIN) connectors

REMA's DIN 80, DIN 160 and DIN 320 connectors are rated at 80 A, 160 A and 320 A respectively, with a rated voltage of 150 V. REMA explains that its coding system has two purposes:

  • Wet or dry coding: a coding pin prevents a flooded ("wet") battery being connected to a charger for gel ("dry") batteries or vice versa, a mismatch REMA warns can destroy the battery, while still allowing either battery type to connect to the truck.
  • Voltage coding: a hexagonal coding pin is set to one of six voltages from 24 V to 96 V, shown in a window in the housing, so plugs and sockets of different voltages cannot be mated.

Anderson SB connectors

Anderson Power Products' SB connectors use colour-coded, mechanically keyed housings. Anderson's recommended voltage colour key is:

Voltage 12 V 18 V 24 V 36 V 48 V 72 V 80 V 96 V 120 V 144 V
Housing colour Yellow Orange Red Grey Blue Green Black Brown Purple White

Anderson rates SB connectors for use up to 600 V and describes the colours and keys as identifiers, so the colour is a convention rather than a limit. The SB family comes in several sizes (such as SB50, SB120, SB175 and SB350) with different current ratings; confirm the size and colour of the existing connector from a photograph.

Charging and watering

Flooded (PzS and PzB) batteries

EnerSys's instructions for its Perfect Plus flooded traction batteries include:

  • Charge after every discharge.
  • Top up with purified water towards the end of charge, not before charging. The electrolyte level must never fall below the top of the separators; when a battery is commissioned with the level below that point, it is first topped up to the separators and then charged.
  • Do not add water in the first 10 cycles.
  • Nominal electrolyte specific gravity is 1.29 kg/l at 30 °C, with a correction of −0.0007 kg/l per °C.
  • Equalising charges are needed after deep discharges, repeated incomplete recharges and charges on an IU characteristic, at a current not exceeding 5 A per 100 Ah of rated capacity.

Single-point watering systems fill all cells from one connection; EnerSys's instructions for these specify filling shortly before the end of a full charge.

Opportunity charging

Opportunity charging means topping up the battery during breaks. ZVEI's leaflet on traction battery service life warns that opportunity charging without electrolyte mixing or regular equalising charges results in acid stratification, with increased corrosion and damage to the active material. EnerSys notes that electrolyte circulation systems are particularly beneficial for boost or opportunity charging.

Ventilation

Flooded batteries release hydrogen during charging. IEC 62485-3 requires battery charging areas to be ventilated to keep hydrogen below 4% by volume and gives a formula for the required airflow based on cell count and charger output. Its worked example for a 48 V, 24-cell flooded battery on an 80 A charger gives 28.8 m³/h.

Flooded, gel and lithium-ion compared

Feature Flooded (PzS/PzB) Gel VRLA (PzV) Lithium-ion
Watering Regular topping up None required (Hawker Evolution: "never refill with water") None required (Toyota)
Opportunity charging Possible with electrolyte mixing and equalising Not allowed on EnerSys Hawker Evolution gel batteries Supported; EnerSys NexSys iON allows opportunity charging
Equalising Required periodically Follow the manufacturer's charging instructions Not required (Toyota)
Weight Heavy; forms counterweight Heavy Lighter cells; counterweight built in to meet truck weight (Toyota)
Integration Standard connector and charger Charger must be gel-specific (REMA dry coding) Battery management system communicates with truck and charger (Toyota)
Lab cycle life (ZVEI, IEC/EN 60254-1 test) Typically 1,500 cycles Typically 900 cycles Manufacturer data

ZVEI stresses that laboratory cycle figures cannot be transferred directly to service life, and recommends that discharge does not exceed 80% of nominal capacity; deeper discharges severely shorten service life.

What to send in an RFQ

Data Why it is needed
Truck make, model and serial number Identifies compartment, weight range and approved battery options
Photo of the truck data plate Battery voltage, minimum and maximum battery weight
Photo of the existing battery label Cell type, cell count, capacity, manufacturer
Voltage and capacity (Ah C5) Defines the cell count and cell size
Tray length × width × height, and cable exit position The tray must fit the compartment
Connector type, size and colour, with photo REMA or SB, voltage coding
Charger make, model and output Charger must suit the battery technology and capacity
Shift pattern and charging practice Single shift, multi-shift, opportunity charging
Watering system required Single-point watering or manual
Technology preference Flooded, gel or lithium-ion (lithium subject to truck manufacturer approval)

Browse forklift and traction batteries and industrial batteries, or send the data above through the battery requirement form. Traction batteries can be consolidated with other parts in a shipment where dangerous goods rules allow; see how to ship batteries internationally.

References

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