Batteries, such as lithium batteries, power many consumer electronic devices. Important market differentiation metrics between available batteries are generally related to how long a battery can last in a particular application scenario. Most consumer electronics operate with low to moderate current draw, resulting in battery discharge durations that can be measured in hours. In such applications, discharge rates are typically some fraction of total battery capacity, e.g., between C/2 and C/10 where C is the battery capacity. Consumers also demand continuous and accurate prediction of the discharge duration they can expect. Therefore, Battery Management Systems (BMSs) comprised of a series of analog measurement and computer logic chips monitor the battery status, make decisions about battery operation, such as when to start and end charging, when to issue warnings to users, etc., and conduct continuous estimations of battery capacity, state of charge, and expected time durations for charge and discharge. The Smart Battery System (SBS) specification used by most BMS systems, calls for discharge duration calculations to be made and presented in terms of minutes. For low to moderate discharge rate applications, such estimates of discharge duration in minutes can be made accurately and are sufficiently granular to be useful.
There are, however, emerging applications where high power battery packs are discharged at very high rates. These applications most commonly contain rechargeable Lithium batteries used to operate electrical equipment for short durations. One example of such an application is a battery backup power supply used to maintain a computer system in the event of a power failure. In such applications, discharge rates can exceed battery capacity by a significant factor, e.g., 10 C, where C is the battery capacity. At such discharge rates, these applications will can potentially discharge the battery in a time period as short as 3 to 5 minutes. Such rapid discharging creates an extreme amount of heat. In some cases, the heat can be enough to melt the battery and cause a catastrophic failure, e.g., a fire and/or explosion. Therefore, most BMS include a thermal safety feature that monitors battery temperature and shuts off or interrupts discharging when the battery heats to a certain temperature. While these thermal safety features greatly improve the safety and reliability of the battery, they can cause the discharge duration estimates calculated by the BMS to be inaccurate since the thermal limit may be reached before the available stored energy of the battery is completely depleted. Furthermore, when batteries are discharged in only a few minutes, discharge duration estimates calculated in minutes do not provide useable information. Hence, there is a need for improved methods and systems for estimating battery discharge time duration during high-rate battery discharging.