IEC TS 61044:2021

Opportunity charging of lead-acid traction batteries

IEC TS 61044:2021(E) covers opportunity charging of lead-acid traction batteries, i.e., the use of idle time during a working period to increase the state of charge (SoC) so as to extend the daily working period of a lead-acid traction battery while at the same time avoiding an excessive depth of discharge.
This document specifies requirements for the use of opportunity charging of lead-acid traction batteries of vented and valve regulated types when the battery manufacturer has not provided alternative specific operating procedures.

General Information

• Status: Published
• Publication Date: 04-Aug-2021
• ICS: 29.220.20 - Acid secondary cells and batteries
• ICS: 29.220.99 - Other cells and batteries
• Technical Committee: TC 21 - Secondary cells and batteries
• Drafting Committee: WG 3 - TC 21/WG 3
• Current Stage: PPUB - Publication issued
• Start Date: 05-Aug-2021
• Completion Date: 27-Aug-2021

Relations

• Replaces: IEC TR 61044:2002 - Opportunity-charging of lead-acid traction batteries
• Effective Date: 05-Sep-2023

IEC TS 61044:2021 - Opportunity charging of lead‑acid traction batteries (Overview)

IEC TS 61044:2021 provides guidance and requirements for opportunity charging of lead‑acid traction batteries used in industrial vehicles and similar applications. The Technical Specification covers both vented lead‑acid batteries and valve regulated lead‑acid (VRLA) batteries, and is intended to be used when the battery manufacturer has not provided specific operating procedures. Its purpose is to extend daily operating time by using idle periods to increase the State of Charge (SoC) while avoiding excessive depth of discharge and premature battery deterioration.

Key topics and technical requirements

• Scope & applicability: Applies to vented and VRLA lead‑acid traction batteries where no manufacturer instructions exist.
• SoC and depth of discharge (DoD):
  • SoC expressed as percentage of rated capacity.
  • Excessive discharge thresholds (for this document unless manufacturer states otherwise): vented = 80% DoD, VRLA = 60% DoD.
  • Opportunity charging at SoC > 70% is less effective and can increase temperature and water loss.
• When to initiate opportunity charging:
  • Preferably after at least 30% of rated capacity has been discharged.
  • For high energy‑throughput / high temperature applications, initiate only after ≥ 40% discharge.
• Charging equipment:
  • Self‑compensating chargers are preferred for opportunity charging.
  • Non‑self‑compensating chargers must not be used for VRLA batteries.
  • Charger current‑voltage‑time characteristics should follow battery manufacturer recommendations for VRLA.
• Operational safeguards:
  • Ventilation requirements for vented batteries.
  • Temperature monitoring - elevated temperatures accelerate ageing.
  • Electrolyte agitation recommended for vented batteries to avoid acid stratification.
• Regular full charges:
  • Generally, perform at least one regular/complete charge every working day (exceptions require manufacturer consultation).
• Planning & warranty:
  • Assess energy balance and duty cycle before implementing opportunity charging.
  • Discuss warranty and lifecycle implications with the battery manufacturer because increased energy turnover can affect battery life.

Applications and users

IEC TS 61044 is practical for:

• Fleet managers and operators of forklifts, airport ground support, warehouse vehicles and other industrial transport.
• Battery maintenance engineers and charging system designers.
• Facility managers planning on‑shift charging strategies to extend run time without battery swaps.
• OEMs and integrators specifying chargers and battery management procedures.

Related standards

• IEC 62485‑3:2014 - Safety requirements for secondary batteries and battery installations (Traction batteries).

Use IEC TS 61044:2021 when implementing opportunity charging to balance increased daily availability with safe operating limits for lead‑acid traction batteries. Always prioritize the battery manufacturer’s specific instructions where available.

Standards Content (Sample)

IEC TS 61044 ®
Edition 1.0 2021-08
TECHNICAL
SPECIFICATION
Opportunity charging of lead-acid traction batteries
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IEC TS 61044 ®
Edition 1.0 2021-08
TECHNICAL
SPECIFICATION
Opportunity charging of lead-acid traction batteries

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.220.20; 29.220.99 ISBN 978-2-8322-1006-7

– 2 – IEC TS 61044:2021 © IEC 2021
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Planning the implementation of opportunity charging . 7
5 Operational procedures . 8
5.1 General . 8
5.2 Charging conditions . 8
5.3 Regular charges . 8
5.4 Ventilation. 9
5.5 Temperature . 9
5.6 Examples of discharge and charge profiles . 9
Bibliography . 12

Figure 1 – Examples of discharge and charge profiles of vented lead-acid batteries . 10
Figure 2 – Example of discharge and charge profiles of valve regulated lead-acid
batteries . 11

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPPORTUNITY CHARGING OF LEAD-ACID
TRACTION BATTERIES
FOREWORD
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IEC TS 61044 has been prepared by IEC technical committee 21: Secondary cells and
batteries. It is a Technical Specification.
This first edition cancels and replaces the second edition of IEC TR 61044 published in 2002.
This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the recommended depth of discharge for opportunity charging has been adjusted;
b) a distinction is made between valve regulated lead-acid batteries (VRLA) and vented lead-
acid batteries.
– 4 – IEC TS 61044:2021 © IEC 2021
The text of this Technical Specification is based on the following documents:
Draft Report on voting
21/1081/DTS 21/1088/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement,
available at www.iec.ch/members_experts/refdocs. The main document types developed by
IEC are described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
Lead-acid traction batteries find a widespread application in industrial transportation vehicles
because of their particular properties of providing a reliable power supply source with a very
low environmental impact.
In such applications, both monitoring and power management by electronic means have made
great strides not only on the discharge side of the energy balance but during charging as well.
This progress permits refuelling, i.e., charging of a lead-acid traction battery in a well-
controlled manner during idle periods in the course of a working schedule.
As a result, the total capacity or ampere-hour output of the lead-acid battery increases per
working day substantially beyond the manufacturer's maximum recommended value.
However, such opportunity charging will provide improved capital efficiency only if adequate
precautions are taken to prevent premature deterioration of the state of the lead-acid traction
battery caused by such a practice.
This document is intended to present requirements, derived from the field experience of
battery manufacturers in general and from opportunity charging of lead-acid traction batteries
...