SAE J3012_202607

This SAE Standard applies to 12-volt 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 recommendations, 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 together with CO2 and other emissions. Many newer vehicles therefore utilize 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 system. These include the traditional loads such as lights, fans, entertainment, sensors, and the ignition system, but with increasingly added loads such as electrical steering and brakes. The battery must also provide many more cranking starts compared to conventional vehicle operation in which the engine stays in continuous charging operation during a driving cycle. Once the engine has restarted from a stop event, the generating system must recharge the battery sufficiently to keep it in continuous operating condition. Because of the extra discharges in urban or suburban traffic, start-stop batteries typically operate in a partially discharged condition that leads to an increased charge acceptance during charging opportunities. However, this remaining discharge from partial discharge tends to become more resistant to charge with stand unless special charge enhancement properties are added to stop-start batteries or special charging methods are added periodically. 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 power to provide instantaneous starting, sufficient capacity to supply electrical power during limited stops, 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 stop the engine in a position to restart more rapidly and delay recharging after starts to allow more power for early acceleration. A battery employed in a start-stop application may be asked to: Support the total electrical load demand during the drive cycle each time the internal combustion engine (ICE) is temporarily stopped (such as at a stop light). Be able to restart a “warm” engine in a reduced charge state multiple times over a drive cycle. Accept recharge energy as efficiently and quickly as possible in order to maintain sufficient power for future electrical demand events. Work in conjunction with a Battery Management System (BMS) that includes a battery status monitoring device that supplies information to the vehicle computer to only allow start-stop activity when the battery is in a satisfactory condition and there are no compromises to the vehicle performance and the safety and comfort of vehicle occupants. It is typically seen that start-stop functions in a temperature range that is neither too cold nor too warm for vehicle occupants unless other means are provided to keep the occupants comfortable. The BMS should also determine battery defects and end of life if a replacement is needed. The BMS ensures the battery gives reliable starting and is safe and non-intrusive for start-stop functioning and normal vehicle operation. It is also a general expectation that start-stop batteries provide similar or better service life than the batteries serving traditional ICE vehicles. Of course, like a traditional ICE vehicle battery, the start-stop battery needs to be able to support the vehicle loads during an emergency or the loss of the vehicle charging system. 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. Flooded lead-acid batteries used in traditional vehicles without start-stop have been found to give inadequate life performance in start-stop operation. Therefore, start-stop vehicle manufacturers almost entirely specify more robust 12-volt lead-acid battery variations (AGM - absorbent glassmat batteries or EFB - enhanced flooded batteries). Testing as outlined in this document has been targeted at these lead-acid battery 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. It has been observed that there are normally two types of start-stop vehicle systems. The typical type uses the same cabling and starter path for warm and cold starting. The second type uses a separate higher resistance route to reduce the starter current for warm starts while using the normal route for cold starts. Technology to increase vehicle and battery efficiencies is changing rapidly. It is expected that batteries related to start-stop performance will have increased performance to meet these demands. It is therefore recommended that this document be reviewed as needed to keep it relevant.