Laptop battery does not charge
With the growing complexity of laptops, notebooks and netbooks, figuring out why a laptop battery does not charge is not easy. Laptop batteries that suddenly die or notifications like ”laptop battery not recognized” trigger valid reasons for suspicion. Even more – simply replacing a laptop battery is an expensive affair and certainly not always the solution. Nowadays there are many components involved in charging a laptop battery. In this story you’ll find a simplified approach to narrowing down a laptop battery problem and possible leads to a solution.
Simple laptop battery charging diagnosis
The simplified diagnosis assumes the following;
1) Laptop works on AC power – laptop battery doesn’t charge.
2) Laptop battery has worked before in the same laptop
The approach assumes the smart battery system architecture developed by Duracel and Intel. A DELL Latitude D610 business laptop is used as example.
Although the information here might not apply in all cases, it still might shed light on reasons why a laptop battery does not charge.
The diagnosis approach is based on the observation that all laptop battery charging components are active when the laptop is powered off with the AC power adapter connected. This is true for most laptops and eliminates the involvement of the main processor in charging a laptop battery.
Laptop battery charging is managed by a second processor on the laptop motherboard. In this approach the second processor is identified as the POST (Power On Self Test) controller. The controller executes initial test during power-on and manages laptop battery charging. Although this might not apply for all laptops, the observation mentioned earlier still stands.
When the laptop is powered-on information about laptop battery charging can be monitored through either through the BIOS setup screen or for example in Windows or Linux.
The laptop battery charging diagram below shows various components involved in charging a laptop battery. The blue and red marked text indicates click-able text and loads pages with more information.
Laptop battery charging diagram
Diagnosis diagram when a laptop battery is not charging
Laptop battery charge controller and program code
The POST controller (Power On Self Test) is a second processor or CPU on the laptop motherboard. It remains active when a laptop is powered down unless the AC power adapter is disconnected. The POST controller manages laptop battery charging and communicates with the laptop battery and AC power adapter.
The POST controller also runs test when the laptop is powered on. For DELL laptops the POST controller outputs diagnostic codes through the CAPS, NUM and SCROLL lock lights. After POST tests are completed successfully it starts the main CPU which executes BIOS program code for further testing.
The POST controller for a DELL Latitude D610 is the SMSC LPC47N354 – MacAllen III – Ultra IO controller. Unfortunately there’s little public information available but it seems this chip executes POST functions using a 8051 based micro controller. The latter is a highly popular multi-purpose embedded CPU capable of doing quite a bit of work in the lower dungeons of the DELL Latitude D610 laptop.
Laptop battery cell charging controller
The battery controller in DELL Latitude D610 batteries is the custom made BQ20864 – called a battery gauge – from Texas Instruments. The battery gauge chip tracks battery cell charge and discharge information for the laptop battery charge control circuit. There’s no public information available about this particular battery charge controller – most likely it’s protected information only available to DELL.
Windows 7 has native support for accessing battery gauge chip registers, however the feature seems to have maturity problems.
Laptop battery charge control circuit
The laptop battery charge control circuit supplies power to the laptop battery – it handles the actual charging of the battery cells in the laptop battery. The main functions performed by this circuit, among others:
- DC-DC voltage conversion from the AC power adapter to the Laptop batteries
- Start, Control and Stop the battery charging stages from bulk charge to trickle charge
- Communicate with the slave which is the charging controller in the laptop battery
- Communicate with the master which is the POST controller
For the DELL Latitude D610 the MAX1535B Battery Charger chip is the center of this circuit. The DC-DC conversion produces quite a bit of heat making it easy to locate this circuit when charging the laptop battery while powered down.
Laptop battery charging indicator LED
The laptop battery charging indicator is a multicolor LED emitting flash codes in several colors indicating the status of the charging process.
The laptop processor executes BIOS program code after the POST controller completes the Power On Self Tests. During BIOS execution a laptop can generate diagnostic codes on the screen or through beeps. After BIOS tests are completed successfully the laptop processor tries to boot the operating system on the hard disk, CDROM or USB drive / stick.
The DELL Latitude D610 has a Intel Pentium M processor.
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