Specifications

Smart Battery Charger Specification
SBS Implementers Forum -Page 5- Revision 1.1
4.2. Smart Battery Charger Types
Two types of Smart Battery Chargers are defined: Level 2 and Level 3. This document defines a particular
set of characteristics and minimum command set for each type of Smart Battery Charger. All Smart
Battery Chargers communicate with the Smart Battery using the SMBus; the two types differ in their
SMBus communication mode and whether they modify the charging algorithm of the Smart Battery. Level
3 Smart Battery Chargers are supersets of Level 2 chargers and as such support all Level 2 charger
commands. See Section 6 for more detailed characteristics the charger types.
Note: Level 1 Smart Battery Chargers were defined in the version 0.95a specification. While they can
correctly interpret Smart Battery end-of-charge messages minimizing over-charge, they do not provide
truly chemistry independent charging. They are no longer defined by the Smart Battery Charger
specification and are explicitly not compliant with this and subsequent Smart Battery Charger
specifications.
4.2.1. Level 2 Smart Battery Charger
The Level 2 or Smart Battery controlled Smart Battery Charger interprets the Smart Battery's critical
warning messages, and operates as a SMBus slave device that responds to ChargingVoltage() and
ChargingCurrent() messages sent to it by a Smart Battery. The charger is obliged to adjust its output
characteristics in direct response to the ChargingVoltage() and ChargingCurrent() messages it receives
from the battery. In Level 2 charging, the Smart Battery is completely responsible for initiating the
communication and for providing the charging algorithm to the charger. The Smart Battery is in the best
position to tell the Smart Battery Charger how it needs to be charged. The charging algorithm in the
battery may simply request a static charge condition or may choose to periodically adjust the Smart Battery
Charger's output to meet its present needs. A Level 2 Smart Battery Charger is truly chemistry
independent, and since it is defined as a SMBus slave device only, the Smart Battery Charger is a relatively
inexpensive and easy to implement device.
4.2.2. Level 3 Smart Battery Charger
The Level 3 Smart Battery Charger not only interprets the Smart Battery's critical warning messages, but is
allowed to act as a SMBus master device. In Level 3 charging, the Smart Battery is not necessarily
responsible for initiating the communication of ChargingCurrent() and ChargingVoltage() values or for
providing the charging algorithm to the charger. The Level 3 Smart Battery Charger may act as a slave or
poll the Smart Battery to determine the charging voltage and current the battery desires, and then
dynamically adjust its output to meet the battery's charging requirements. This method of Level 3 charging
maintains the chemistry independence property of the charger since Smart Battery is in the best position to
tell the Smart Battery Charger how it wants to be charged.
A Level 3 Smart Battery Charger is free to implement an alternative specialized charging algorithm. It may
also interrogate the Smart Battery for any other relevant data, such as time remaining to full charge, battery
temperature or other data used to control proper charging or discharge conditioning. For example, a
medical device with stricter temperature limits than the Smart Battery's self-contained charging algorithm,
may use a Level 3 Smart Battery Charger that factors in the battery's reported temperature into its charging
algorithm.
The Level 3 Smart Battery Charger may be chemistry independent like the Level 2 charger. Because it
supports SMBus Master Mode, the Level 3 Smart Battery Charger is more complex, thus more expensive
Charger Type by SMBus mode and charge algorithm source.
Charge Algorithm
SMBus mode
Battery Modified from Battery
Slave only Level 2 Level 3
Slave/Master Level 3 Level 3