IEC TS 62257-341:2026

Renewable energy off-grid systems - Part 341: Selection of batteries and battery management systems for stand-alone electrification systems - Specific case of automotive flooded lead-acid batteries available in developing countries

IEC TS 62257-341:2026 proposes simple, inexpensive, comparative tests to determine which types of flooded lead-acid automobile batteries are acceptable for use in PV electrification systems.
It could be particularly useful for project implementers to test in laboratories of developing countries the capability of locally made car or truck batteries to be used for their project.
The tests provided in this document allow assessment of the batteries' performances according to the general specification and batteries associated with their smart battery charging systems (SBCS) in a short time and with common technical means. They can be performed locally, as close as possible to the operating conditions of the real site.
The document also provides recommendations and installation conditions to ensure the life and proper operation of the installations as well as the safety of people living in proximity to the installation.
This document offers guidelines and does not replace any existing IEC Standard on batteries.
This first edition cancels and replaces the second edition of IEC TS 62257-8-1 published in 2018. This edition includes the following significant technical changes with respect to IEC 62257‑8‑1:2018:
- increase of the applicable voltage levels and removal of the 100 kW power limit;
- removal of the word "small" from the description of these systems.

General Information

• Status: Published
• Publication Date: 05-May-2026
• ICS: 27.160 - Solar energy engineering
• ICS: 29.220.20 - Acid secondary cells and batteries
• Technical Committee: TC 82 - Solar photovoltaic energy systems
• Drafting Committee: JWG 1 - TC 82/JWG 1
• Current Stage: PPUB - Publication issued
• Start Date: 06-May-2026
• Completion Date: 15-May-2026

Relations

• Replaces: IEC TS 62257-8-1:2018 - Recommendations for renewable energy and hybrid systems for rural electrification - Part 8-1: Selection of batteries and battery management systems for stand-alone electrification systems - Specific case of automotive flooded lead-acid batteries available in developing countries
• Effective Date: 05-Sep-2023

Overview

IEC TS 62257-341:2026 is a Technical Specification developed by the International Electrotechnical Commission (IEC) that focuses on renewable energy off-grid systems, specifically the selection and evaluation of batteries and battery management systems for stand-alone electrification projects. This document addresses the unique scenario of using automotive flooded lead-acid batteries that are widely available in developing countries, providing valuable guidance for photovoltaic (PV) and other off-grid electrification applications.

The standard introduces simple, low-cost comparative test methods to assess the suitability and endurance of locally sourced automotive lead-acid batteries when repurposed for PV off-grid systems. These methods are intended to be easily performed in basic laboratories and reflect typical installation and operational environments. Additionally, the document offers recommendations on installation practices, maintenance, and safety protocols to maximize battery lifespan and ensure the well-being of those near the installations.

Key Topics

• Battery Selection Criteria: Guidelines for identifying suitable automotive flooded lead-acid batteries through practical comparative tests, allowing implementers to select batteries that will deliver reliable performance under typical off-grid conditions.
• Laboratory Comparative Tests: Step-by-step test sequences that evaluate endurance, compatibility with smart battery charging systems (SBCS), and storability (self-discharge and recovery after storage).
• Battery and Charging System Compatibility: Recommendations for ensuring that selected batteries and SBCS work well together to optimize system efficiency, minimize maintenance, and extend service life.
• Installation and Safety: Practical advice to ensure safe battery handling, electrolyte management, appropriate housing, and protection against electrical hazards.
• Maintenance and Water Consumption: Guidance on monitoring and maintaining electrolyte levels, including water consumption estimates for battery upkeep.

Applications

IEC TS 62257-341:2026 is primarily intended for project developers, procurement agencies, and implementers involved in rural or off-grid electrification using renewable energy, particularly in developing regions where locally manufactured automotive batteries are an accessible resource. Key application areas include:

• Rural PV Electrification Projects: Testing and selection of automotive batteries for small-scale solar home systems or community micro-grids.
• Hybrid Off-Grid Power Systems: Use in systems that combine renewable sources (solar, wind, or hydro) with conventional generators, where robust energy storage is essential.
• Local Laboratory Testing: Enables laboratories in developing countries to rapidly, cost-effectively, and accurately evaluate battery options under site-relevant conditions.
• Safe and Sustainable Deployment: Ensures that battery installations follow safety and environmental best practices, reducing risks to users and communities.

By following the comparative testing procedures described in the standard, implementers can confidently choose batteries that are more likely to withstand demanding off-grid service, thus reducing the risk of premature failure and minimizing life cycle costs.

Related Standards

IEC TS 62257-341:2026 is part of the IEC 62257 series, which addresses various aspects of renewable energy off-grid systems for rural and remote applications. Other relevant standards and guidelines include:

• IEC TS 62257-6: Recommendations for acceptance, operation, maintenance, and replacement of renewable energy and hybrid systems.
• IEC 60050-482: International Electrotechnical Vocabulary covering terms for primary and secondary cells and batteries.
• ISO 7010: Standard for graphical safety symbols, relevant for battery installation signage and user information.

This Technical Specification updates and replaces the previous IEC TS 62257-8-1, expanding the scope to allow for greater voltage levels and removing previous limitations on system size, supporting broader application for off-grid electrification.

For detailed procedures and local adaptation, users are encouraged to consult the full IEC TS 62257-341:2026 document and related references in the IEC 62257 series.

Standards Content (Sample)

IEC TS 62257-341 ®
Edition 1.0 2026-05
TECHNICAL
SPECIFICATION
Renewable energy off-grid systems -
Part 341: Selection of batteries and battery management systems for stand-
alone electrification systems - Specific case of automotive flooded lead-acid
batteries available in developing countries
ICS 27.160; 29.220.20 ISBN 978-2-8327-1215-3

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CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Batteries and battery charging system selection. 8
4.1 Battery technical characteristics . 8
4.1.1 Battery cases . 8
4.1.2 Battery terminals . 8
4.1.3 Electrolyte . 8
4.2 Comparative tests . 9
4.2.1 General. 9
4.2.2 Evaluation of the charge and discharge current for testing (I ) . 10
test
4.2.3 Test 1: battery endurance test . 10
4.2.4 Test 2: endurance test for battery and smart battery charging system. 14
4.2.5 Test 3: Battery storability test . 16
5 Documentation . 18
6 Installation and safety rules . 18
6.1 Packing and shipping . 18
6.2 Environment . 19
6.3 Battery accommodation, housing . 19
6.3.1 General. 19
6.3.2 Provision against electrolyte hazard . 19
6.3.3 Prevention of short circuits and protection from other effects of electric
current . 20
6.3.4 Battery enclosures . 21
6.4 Final inspection . 22
6.5 Safety. 22
6.5.1 Safety provisions . 22
6.5.2 Safety information . 22
6.6 Administrative formalities. 22
6.7 Recycling . 23
Bibliography . 24

Figure 1 – Test 1 phases . 11
Figure 2 – Phase A battery endurance test . 12
Figure 3 – Phase B battery endurance test . 13
Figure 4 – Test 2 phases . 15
Figure 5 – Phase C battery – SBCS endurance test . 16
Figure 6 – Test 3 phases . 17
Figure 7 – Phase D storability test . 17
Figure 8 – Marking for spillage prevention . 19

Table 1 – Testing procedure . 9
Table 2 – Evaluation of charge and discharge current (I ) . 10
test
Table 3 – Voltage regulation variation with temperature (examples) . 10

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Renewable energy off-grid systems -
Part 341: Selection of batteries and battery management systems for
stand-alone electrification systems - Specific case of automotive flooded
lead-acid batteries available in developing countries

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC TS 62257-341 has been prepared by IEC technical committee 82: Solar photovoltaic energy
systems. It is a Technical Specification.
This first edition cancels and replaces the second edition of IEC TS 62257-8-1 published in
2018. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to
IEC 62257-8-1:2018:
a) increase of the applicable voltage levels and removal of the 100 kW power limit;
b) removal of the word "small" from the description of these systems.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
82/2562/DTS 82/2602/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/publications.
A list of all parts in the IEC 62257 series, published under the title Renewable energy off-grid
systems, can be found on the IEC website.
Future documents in this series will carry the new general title as cited above. Titles of existing
documents in this series will be updated at the time of the next edition.
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, or
– revised.
INTRODUCTION
The IEC 62257 series provides technical standardization to different stakeholders (including
but not limited to project developers, financing agencies, testing agencies, installers) involved
in electrification projects for access to electricity for those not solely connected to the regional
grid, through the setting up of off-grid renewable energy and hybrid systems (including micro-
grids) with a voltage less than or equal to 1 000 V for AC (alternating current) or a voltage less
than or equal to 1 500 V for DC (direct current).
Access to electricity is one of the predominant policy actions designed to increase the well-
being of populations, together with access to clean water, improved healthcare, education,
personal advancement and economic development. Increasing access to electricity through
utilization of renewable off-grid electricity also directly or indirectly supports various United
Nations sustainability development goals [1] , depending on the application.
Several strategies can be adopted to implement electrification and improve access to electricity
in rural and urban settings, including the ability for connection to a national or regional electricity
grid. The IEC 62257 series applies to cases where the utility grid is too far away or incapable
to support load, the individual demand centres are too small to make grid access economical:
off-grid solutions provide an economical option, and where autonomous power systems can be
used to supply these services.
The 62257 series is used to
a) choose the right solution for the right place with the optimal technology,
b) design, purchase and install the product(s) and system to optimal compliancy, and
c) operate and maintain the system.
The IEC 62257 Technical Specifications focus on enabling access to electricity to concentrate
on, developing countries. This series shall not be considered as all-inclusive for access to
electricity. That means that the Technical Specifications could be used for rural electrification,
also for electrification of remote sites in developed countries, or any requirement for electricity
access that cannot be met by attaching solely to the national utility grid. The documents promote
the use of renewable energies also allowing other energy sources, such as diesel generators,
to be included as part of a hybrid renewable energy off-grid system.
This consistent set of documents can be considered as a whole, with different parts focusing
on specific aspects of renewable energy off-grid systems. However, several parts are intended
to be read as stand-alone documents depending on their intended application.
IEC TS 62257-100 provides an overview of the various topics covered by this series.
Additionally, the content and scopes of individual documents, available at the website
webstore.iec.ch, provide potential users with the intended application for each document. For
further information on planned documents to be published under the new IEC 62257 numbering
scheme, IEC TC 82 committee members can refer to the annex in the JWG1 Program of Work
circulated after each JWG1 meeting, or to the Planned Work Programme on the www.iec.ch
TC82 website.
One of the main objectives of this series is to provide the minimum sufficient recommendations,
including items for safety, sustainability of systems and at the lowest life cycle cost, relevant to
the renewable energy and hybrid off-grid systems fields of application.
The purpose of IEC TS 62257-341 is to propose tests for automotive lead-acid batteries and
battery management systems used in small PV individual electrification systems. Future parts
of the series will carry a three-digit numbering.
___________
Numbers in square brackets refer to the Bibliography.
1 Scope
This part of IEC 62257, which is a Technical Specification, proposes simple, inexpensive,
comparative tests to determine which types of flooded lead-acid automobile batteries are
acceptable for use in PV electrification systems.
It could be particularly useful for project implementers to test in laboratories of developing
countries the capability of locally made car or truck batteries to be used for their project.
The tests provided in this document allow assessment of the batteries' performances according
to the general specification and batteries associated with their smart battery charging systems
(SBCS) in a short time and with common technical means. They can be performed locally, as
close as possible to the operating conditions of the real site.
The document also provides recommendations and installation conditions to ensure the life and
proper operation of the installations as well as the safety of people living in proximity to the
installation.
This document offers guidelines and does not replace any existing IEC Standard on batteries.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050-482:2004, International Electrotechnical Vocabulary - Part 482: Primary and
secondary cells and batteries
IEC 60050-482:2004/AMD1:2016
IEC 60050-482:2004//AMD2:2020
IEC TS 62257-6, Recommendations for renewable energy and hybrid systems for rural
electrification - Part 6: Acceptance, operation, maintenance and replacement
ISO 7010, Graphical symbols - Safety colours and safety signs - Registered safety signs,
available at https://www.iso.org/obp
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-482 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1
secondary cell
cell that is designed to be electrically recharged
Note 1 to entry: The recharge is accomplished by way of a reversible chemical reaction.
[SOURCE: IEC 60050-482:2004, 482-01-03]
3.2
storage battery
secondary battery
two or more secondary cells connected together and used as a source of electric energy
3.3
lead-acid battery
storage battery in which the electrodes are made mainly from lead and the electrolyte is a
sulphuric acid solution
3.4
terminal
pole
conductive part provided for the connection of a cell or battery to external conductors
3.5
density
volumic mass of electrolyte
Note 1 to entry: The density is expressed in kg/dm .
Note 2 to entry: Density is also defined as a dimensionless magnitude expressing the ratio of the electrolyte mass
to the water mass occupying the same volume at 4 °C.
3.6
electrolyte
liquid or solid substance containing mobile ions that render it ionically conductive
Note 1 to entry: The electrolyte can be liquid, solid or a gel.
[SOURCE: IEC 60050-482:2004, 482-02-29, modified – "May" replaced with "can" in the note
to entry.]
3.7
dry charged battery
state of delivery of some types of secondary battery where the cells contain no electrolyte and
the plates are dry and in a charged state
[SOURCE: IEC 60050-482:2004, 482-05-30]
3.8
self-discharge
phenomenon by which a cell or battery loses energy in other ways than by discharge into an
external circuit
[SOURCE: IEC 60050-482:2004, 482-03-27]
3.9
nominal capacity
suitable approximate quantity of electricity used to identify the capacity of a cell or a battery
Note 1 to entry: The nominal capacity is usually expressed in ampere-hours (Ah).
3.10
rated capacity
quantity of electricity, declared by the manufacturer, that a cell or a
battery can deliver under specified conditions after a full charge
Note 1 to entry: The rated capacity shown on the battery label is given for a discharge period, which depends on
the technology used in the battery.
Note 2 to entry: The capacity of a battery is higher when it is discharged slowly. For example, variations are in the
order of 10 % to 20 % between a capacity measured over 5 h and a capacity measured over 100 h.
3.11
ambient temperature
temperature of the medium in the immediate vicinity of a battery
3.12
initial charge
commissioning charge given to a new battery to bring it to the fully charged state
3.13
cycling
set of operations that is carried out on a secondary cell or battery and is
repeated regularly in the same sequence
Note 1 to entry: In a secondary battery, these operations may consist of a sequence of a discharge followed by a
charge followed by a discharge under specified conditions.
[SOURCE: IEC 60050-482:2004, 482-05-28]
4 Batteries and battery charging system selection
4.1 Battery technical characteristics
4.1.1 Battery cases
Battery cases shall be made of suitable materials capable of withstanding impacts and shocks
and resistant to acid.
4.1.2 Battery terminals
Terminals shall be protected against accidental short circuits. Positive and negative polarities
shall be identified.
4.1.3 Electrolyte
The electrolyte for lead-acid batteries is prepared from special sulphuric acid for storage
batteries. It shall be colourless, odourless and free of all insoluble material deposits. As there
is no standard for such an electrolyte, impurity levels shall follow the battery manufacturer's
requirements.
The electrolyte level checking interval varies depending on the following:
– type of battery;
– temperature;
– use;
– regulation algorithms of the charge controller;
– battery's age;
– quality of the distilled water;
– PV resource.
The service interval is determined from the above parameters and the electrolyte reservoir size,
which is a specification of the specific battery used. Care should be used to ensure that the
service interval is within the capability of the maintenance organization.
The batteries shall preferably be designed so that electrolyte levels are able to be checked and
so that distilled water can be added.
NOTE 1 Faradic water consumption for vented batteries:
– When a battery reaches its fully charged state, water electrolysis occurs according to Faraday's law.
Under standard conditions:
3 3
– 1 Ah decomposes H O into 0,42 dm H + 0,21 dm O .
2 2 2
– Decomposition of 1 cm (1 g) H O requires 3 Ah.
An estimation of water consumption of a battery is given by:
– Battery H O (g) consumption = (X Ah charged – Y Ah discharged) × number of cells in battery / 3.
NOTE 2 The number of cells for a 12 V lead-acid battery is 6.
4.2 Comparative tests
4.2.1 General
The proposed comparative tests are designed to identify appropriate batteries taking into
consideration the techno-economic context of the project.
These comparative tests include a sequence of three tests as indicated in Table 1.
All the batteries shall be tested simultaneously in order to ensure that they are tested in the
same conditions (insulation, temperature, etc.).
Table 1 – Testing procedure
Test 2: the couple battery-SBCS is selected with
another endurance test
Test 1: durable batteries are first selected with a
See 4.2.4
battery endurance test
Test 3: in parallel to test 2, the selected batteries are
See 4.2.3
subjected to a storability test
See 4.2.5
The installation rules for batteries provided in Clause 6 are also applicable to test installations.
4.2.2 Evaluation of the charge and discharge current for testing (I )
test
Automotive lead-acid batteries are typically rated at C .
The proposed
...