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How to check the battery charge capacity of a notebook or tablet PC
Published Date : 03 Jun 2005   Last Updated : 09 Nov 2017   Content Ref: TEC401640  


Perform a full charge - full discharge - full charge cycle before you begin to calibrate the smart battery. If this has already been done in the last month then you do not need to do this. For instance, if you have recharged the battery fully and then used the notebook until the battery is flat again and then recharged it again, you do not need to perform a full charge - full discharge - full charge cycle as this will already have been done.


Checking the battery capacity

A shareware program such as BatteryMon can be downloaded (for example, see the PassMark website at: http://www.passmark.com/products/index.htm).

Note: This is shareware and has a 30-day evaluation period. You will need to buy a copy if you wish to register the software and keep it. If you do not want to buy this software you should uninstall it after testing. We have no connection with PassMark.

If using an RM Window Box™ system, log on as Manager. If using a Community Connect® system, you will need to log on as someone who has sufficient rights to run applications. Once installed, click on the small battery icon (third from the left at the top) to view the battery information.

The Percentage Capacity can be determined as follows:

(Full Charge Capacity/Design Capacity) * 100  
e.g. 2190mWh/4000mWh * 100 = 54.75%

Procedure if you cannot run BatteryMon
If the BatteryMon shareware program does not work, please follow the procedure below.

Battery preparation

Before you begin you must fully charge the battery. Do this by leaving the battery charging from its own AC adaptor.

Note: If the battery has already had a full charge - discharge - charge cycle in the last month, then you do not need to do this again.

Check the following:

  1. Check the computer is indicating that it is receiving a charge (normally a flashing LED).
  2. Ensure that the AC adaptor you are using is the correct one. Each AC adaptor is normally labelled with the same serial number as the computer it came with.
  3. Ensure the mains supply is from a known good supply (e.g. use a power socket that is known to be working and is on all the time). In particular, do not use a mains supply in a 'charging trolley' or NoteBus as this may be the cause of the issue.
  4. Do not apply any pressure to the power plug, such as resting the computer on the low voltage DC power plug or allowing the AC adaptor to hang from this plug. This can cause poor contact and can damage the power socket inside the computer.

Testing procedure using BatCal (if BatteryMon test cannot be run)

If using an RM Window Box system, log on as Manager. If using a Community Connect system you will need to log on as someone who has sufficient rights to use Control Panel and run applications.

Download the RM BatCal utility from the Download section below)to the Microsoft® Windows® desktop. This will help you test the battery. Follow the steps below to continue:

  1. Remove the battery from each computer and label it with the serial number of the computer. This is to ensure your warranty is valid, in case you need to return the computer for a warranty repair or battery replacement. For a valid warranty claim, the battery serial number must match RM factory records.
  2. Connect the AC adaptor so that the computer is working from the mains supply.
  3. Remove any PC cards (PCMCIA cards), USB devices and other peripherals.
  4. Disable the internal wireless card, if fitted (usually by means of a switch on the notebook). Wireless operation can reduce battery discharge times by up to 20%. (RM quoted battery life does not include wireless use).
  5. Disable any screensaver (so that you can always watch the screen).
  6. Run the BatCal program.
  7. Click on the Set Slow Discharge button - ensure that Slow Discharge is displayed in bold just below the View Result button.
  8. Click on the Begin Calibration button. The Control Panel - Power Options Properties dialog box will be displayed.
  9. Follow the instructions displayed in the BatCal window, e.g. turn all battery power settings to Never and set the power scheme to Portable/Laptop. If you have very poor battery life, you can also de-activate the Alarms settings, so that the computer does not shut down when it reaches a critical level. This is because an uncalibrated battery can lie about its capacity and cause the notebook to hibernate when it is not actually empty.
  10. Click on OK to close down the Control Panel applet.
  11. Click on the BatCal pop-up dialog box that prompted you to set up the Control Panel settings.
  12. Click on Yes, when asked if you are ready to start the run.
  13. Remove the AC adaptor plug as prompted by the BatCal utility (normally the screen will dim). If your computer has been manually set to a high brightness level when running on battery you should set this to a medium level. High screen brightness will draw more power (e.g. five percent more) than a medium level of brightness.
  14. BatCal should now begin to log the battery charge.
  15. Leave the computer alone - do not close the lid.

The computer will eventually either turn off or hibernate. When this occurs, do the following:

  1. Connect the AC adaptor.
  2. Turn on the computer and log on to Windows.
  3. Run the BatCal program (if it is not already running).
  4. Click on the View Result button to see the length of time that the run lasted.
  5. Keep a copy of the file C:\BatCal.log and rename it to the name of the computer serial number (e.g. rename BatCal.log to WO4285123.log) from which it came. We may require these log files.

Interpretation of BatCal results

The above test should be repeated again to ensure that you obtain consistent results and to ensure the smart battery is calibrated.

The battery life quoted by manufacturers is for a brand new, fully charged battery with wireless disabled, and running on Portable/Laptop power profile using a special industry-standard BatteryMark utility.

The BatteryMark test tends to give slightly longer results than those returned when running BatCal because BatCal is constantly accessing the hard disk. For instance, a quoted battery life for a notebook may be three and a half hours maximum. If BatCal was run on the same notebook, a discharge time of only three hours may be seen for a brand new battery. BatCal is not intended to measure the maximum battery life, but it can be used to give an indication of battery life for comparison purposes between different notebooks and batteries.

Possible Issues

Common causes of poor battery life
  1. Heat - Placing the AC adaptor underneath the notebook during charging seriously degrades the battery over time. Similarly, leaving the notebook on top of a monitor, radiator or car window in direct sunshine are common causes of heat degradation (over a period of months).
  2. Using the battery until it is flat. Lithium-Ion batteries tend to last longer if you avoid using them when they are nearly flat. Try to always charge them well before they become empty (i.e. as often as possible).
  3. Leaving the battery in a fully discharged state. Typically this happens when you repeatedly switch the system on in order to use it for a few minutes longer after it has shut down due to a low battery, and then do not charge the battery for many months. The battery will then not charge due to a safety mechanism in the battery to prevent possible overheating and explosion which may result from charging a fully discharged battery.
  4. Incorrect AC adaptor used. If the wrong AC adapter is used which has too low a voltage or current rating, the notebook may run on the mains but the battery may not charge. RM always label both the AC adaptor and the notebook with the same RM serial number.
  5. Extended use. Lithium-Ion batteries are rated for 250-500 full charge/discharge cycles (depending on cell type used) at which point they will be at 50% capacity. After this they will rapidly deteriorate. All Lithium-Ion batteries have a finite life and will need to be replaced after prolonged use.

Tip: To avoid completely discharging the batteries over long periods when not in use (e.g. school summer holidays), fully charge and remove the batteries from the notebooks and store in a cool place until you next need to use them.

More Information

Tips for improving discharge times

To increase the battery discharge time (maximum running time), try the following:

  1. Set the Control Panel - Power profile to Max Battery and use timeouts to hibernate the system when not being used for more than ten minutes or so.
  2. Set the power settings, so that the screen and hard disk are disabled after five minutes of inactivity.
  3. Reduce the screen brightness as much as you can.
  4. Switch off the wireless card whenever you are not using it.
  5. Disconnect any peripherals, for example if you use a USB flash memory stick, copy any files you need and then unplug it. This can give an extra 20 minutes or so of use.
  6. Do not connect PCMCIA cards (PC cards) unless you need to use them. Remove them when not needed.
  7. Change the Control Panel - Alarm settings to their absolute minimum (e.g. four percent). This can gain an extra ten minutes of use (but the notebook may cut out suddenly if you have a degraded battery).
  8. Do not access a CD more than required. If possible copy or install any software you might need from the CD onto the hard disk and then remove the CD.


FilenameFile SizeDownload
Batcal.exe41 kb Download

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Document Keywords: batteries, fail, dead, calibrate, power, lithium-ion, nickel cadmium, measure, flat, week, poor, last, die, expire, low battery

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