WO2006126022A1

WO2006126022A1 - Battery monitor

Info

Publication number: WO2006126022A1
Application number: PCT/GB2006/050118
Authority: WO
Inventors: Andrea Bennetti; Carl Gordon Thwaite
Original assignee: Absl Power Solutions Limited
Priority date: 2005-05-27
Filing date: 2006-05-23
Publication date: 2006-11-30
Also published as: GB0510877D0; WO2006126022A8

Abstract

A method for calculating the future performance of a rechargeable battery comprises monitoring and recording each change in the level of charge of a battery, when it occurred and the temperature at which the battery was used or stored to provide a history of battery use, and predicting from the history of battery use how that battery will perform under a future sequence of charging cycles. The condition of the battery, based on the calculated remaining cycles at a calculated charge/discharge profile, may be displayed.

Description

Battery monitor

FIELD OF THE INVENTION

The present invention relates to battery life monitoring for indicating the remaining life of a rechargeable battery (such as a lithium ion rechargeable battery) depending on the number of times it has been recharged and the way in which it has been used.

BACKGROUND OF THE INVENTION

A number of methods exist which predict the remaining charge in a battery; however, such methods do not indicate to the user the number of cycles remaining before the battery must be replaced. Certain methods attempt to calculate how many equivalent cycles the battery has completed and subtract from a predetermined total. However, these methods do not allow for actual history of battery usage and are hence inaccurate.

Many devices in current use employ rechargeable batteries, for example, mobile phones, personal digital assistants (PDAs) and global positioning systems (GPS) . These systems often have a battery charge monitor as part of the unit, to indicate the current charge in the battery, but do not generally indicate the number of charge cycles that remain before a given reduction in performance occurs. After a certain number of charging cycles, such batteries typically have reduced performance and eventually have to be replaced. Where performance is critical, it is important to know in advance when it is necessary to replace a battery. For military and space applications, the power unit (including the battery) is generally a discrete item, and its condition must be determined and displayed on the battery itself.

SUMMARY OF THE INVENTION

The present invention allows the remaining lifetime (number of charges) of a rechargeable battery to be predicted in real time based on the usage profiles experienced by the battery. It relates to a system that resides in the battery, and provides an indication of the condition of the battery, permitting the user to determine if the battery requires replacement.

Accordingly, the present invention aims to provide battery life monitoring for indicating the future performance of the battery and displaying the condition of the battery without requiring external apparatus to detect or display the information.

The present invention provides a method for calculating the future performance of a rechargeable battery which method comprises

(A) monitoring and recording each change in the level of charge of a battery, when it occurred and the temperature at which the battery was used or stored to provide a history of battery use, and

(B) predicting from the history of battery use how the battery will perform under a future sequence of charging cycles .

It will be appreciated that, in step (A) , other factors may be monitored and recorded. This knowledge of battery history allows the future use of the battery to be predicted, allowing the prediction of remaining life to be improved with use.

The rechargeable battery is preferably a lithium ion battery.

DETAILED DESCRIPTION OF THE INVENTION

The battery typically contains a memory chip which automatically records changes of charge level with time and temperature. Automatically recording changes in charge may allow the remaining cycle life to be calculated more accurately as it is then possible to build up a more accurate record of the rate of change of the charge during use of the battery. These data may be used to determine the average discharge/charge profile and temperature of operation. Alternatively, abnormal data may be excluded from this calculation based on frequency of occurrence.

The time intervals at which battery use and temperature are recorded may be a few seconds, minutes, hours or days. Alternatively, battery use may be recorded only when the battery is being used, discharged or exposed to a temperature change.

How the battery will perform in a future sequence of charging cycles depends on the history of battery use. The way in which battery history affects the battery' s future performance also depends on the type of battery as some cells maintain a good performance when subjected to multiple deep discharges and others maintain a good performance when subjected to multiple shallow discharges .

For a particular type of battery the number of cycles remaining is determined by considering the depth of discharge, temperature, internal resistance and other parameters. When the behaviour of the battery under different charge/discharge and temperature regimes is well understood, it is possible to calculate the remaining number of cycles until the battery reaches a given capacity limit .

It has been proposed that for a particular type of battery the maximum number of charging cycles can be determined experimentally by testing a number of batteries. This can be used to provide the simplest monitor of remaining battery life and therefore of how long the battery will continue to last. Such a method does not take into account the history of the battery. The present method allows the number of cycles remaining to be calculated based on the actual usage conditions that the battery has experienced, rather than assuming a preset number.

This method typically requires the use of an electronics board comprising system management bus (SMBus) compliant battery electronics and a memory storage that will hold the history of the battery cycles. In addition a microprocessor will be required to allow manipulation of the stored data and calculation of future battery performance. Such electronics may be combined with the safety electronics required by the battery. Typically, a battery is regarded as no longer acceptable for further use when it holds only a proportion of the full initial charge, the acceptability of which proportion varies according to the application for that battery. For example, the space industry or a military application typically require a higher proportion of the level of full charge of a battery whereas, in other applications, a lower proportion of full charge may be acceptable.

EXAMPLES

The invention will be particularly described by way of example only, as follows

Example 1

A lithium ion battery was fully charged to 4.2V per cell. The battery was used at 25⁰C, discharged by 60% and then recharged to full charge ten times over twenty days. The battery was then used at 1O⁰C for twenty days and during that time discharged by 80% and then fully recharged.

The depth of discharge and temperature and other necessary parameters were recorded in the memory. After the final charge, the user requested an indication of the battery expected lifetime. The average depth of discharge and temperature were calculated. The embedded software then used the average values to calculate the number of cycles left until the battery could only be charged to 80% capacity. The number of remaining cycles was 148, which equates to over six months use: therefore the battery condition was indicated as ^Λgood' .

Claims

1. A method for calculating the future performance of a rechargeable battery which method comprises

2. A method according to claim 1 wherein the battery is a lithium ion battery.

3. A method according to claim 1 or claim 2 which further comprises obtaining a visual indication, from the battery, of remaining useful cycles under a prescribed charge/discharge regime.

4. A method according to any of claims 1 to 3 which further comprises predicting from the history of battery use how that battery will perform under a second or further future sequence of charging cycles, and storing, charging and/or discharging the battery in accordance with one of those sequences.

5. A method according to any of claims 1 to 4 which method further comprises rejecting the battery if it no longer holds a predetermined level of charge.

6. A method according to claims 1 to 5 where the history of battery use is recorded in a memory chip in the battery.