J3012_202002 Storage Batteries for Start-Stop Operations



Issuing Committee
This SAE recommended practice applies to 12 V lead-acid storage batteries that are designed specifically for start-stop operations in on-road passenger vehicles or light trucks. Included are definitions of terms, general testing requirements, key performance characteristics, and life testing. Properties not unique to start-stop batteries should be tested according to SAE J537 or other applicable testing protocols.
Increased demands for fuel efficiency and lower environmental impact have fostered efficiency changes in the ways internal combustion engine (ICE) vehicles operate. In particular, time spent stopped in traffic with the vehicle engine at idle is recognized as a key source of wasted fuel, CO2, and other emissions. Many new vehicles are therefore utilizing a relatively cost-efficient method of improving fuel efficiency by stopping the engine when the vehicle is temporarily halted and restarting it when the vehicle needs to be driven or after a limited discharge time. This has come to be called start-stop operation (often also called stop-start, auto-stop, idling stop, idle stop and go, and micro-hybrid). Start-stop operation offers no alternate vehicle propulsion.
Start-stop operation puts increased demands on a vehicle battery. During the many stop periods when there is no output coming from the vehicle charging system, it must exclusively power the various loads in the vehicle electrical system. It must also provide many more cranking starts compared to conventional vehicle operation in which the engine stays in continuous operation during a driving cycle. Once the engine has re-started, the alternator must recharge the battery sufficiently to keep it in continuous operating condition. Because of the extra discharges in urban traffic, start-stop batteries typically operate in a partially discharged conditon that leads to an increased charge acceptance during charging opportunities.
Batteries that satisfy the demands for this type of operation need to have enhanced electrical properties compared to typical batteries used in traditional internal combustion vehicles. Key performance features of start-stop batteries are high power to provide instantaneous starting, good charge acceptance to keep the battery in acceptable operating condition, and resistance to cranking and capacity loss in partial discharge shallow cycling. Besides enhanced batteries, vehicles with start-stop operation need more robust starting, charging, and control systems that work to keep the battery and vehicle in proper start-stop operation to achieve the vehicle fuel efficiency/emissions ratings. Start-stop vehicles may also deliver braking regeneration to capture momentum energy and stop the engine in a condition to restart more rapidly. Start-stop vehicles normally have battery monitoring systems (BMS) that work in conjunction with the vehicle computer to ensure reliable starting and safe and non-intrusive start-stop function during vehicle operation.
This document of recommended practices therefore focuses on functional definitions and tests of those batteries that reflect the demands for usage in start-stop operation. Batteries with various chemistries or combinations of batteries have been proposed for this type of operation. Up until this time, start-stop vehicle manufacturers almost entirely use lead-acid battery variations (AGM-absorbent glassmat/EFB-enhanced flooded); therefore, testing as outlined in this document has been targeted at these lead-acid characteristics. If there is a battery combination other than a single battery intended to be used in a start-stop vehicle, it should be tested as a single unit rather than separate items with the agreement of the supplier and user.
Technology to increase vehicle efficiencies is changing rapidly. It is expected that batteries related to start-stop performance will have changing demands in the near future. It is therefore recommended that this recommended practice document be reviewed on a frequent basis to keep it relevant.
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SAE International Recommended Practice, Storage Batteries for Start-Stop Operations, SAE Standard J3012_202002, Issued February 2020, https://doi.org/10.4271/J3012_202002.
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Feb 10, 2020
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Recommended Practice