Laptop Does Not Boot from a Charged Battery

[alphaa10]

This HP laptop, model DV2125NR, running XP Media Center, cannot boot from its battery, alone. Yet, the battery is known to be in good condition and fully charged.

To make matters more interesting, the laptop can boot with only its AC adapter (that is, without a battery installed), and can boot with both the AC adapter and the (good) battery installed. But not from its battery, alone.

The battery-only configuration does permit the CPU fan to run (airflow present), does permit the hard drive to run, and displays operating LEDs but allows no screen display. In some way, the laptop fails to sense the battery has a full charge and allow the boot process to continue, so perhaps the charging circuit interconnection is faulty, in some way.

In addition to the original battery, a second (new) battery was purchased to aid in diagnostics. However, that battery, when fully charged and used in a battery-only configuration, does exactly what the original battery does-- runs the fan, hard drive and system status LEDs, but halts the boot process.

What do you think is wrong?

 

[utroz]

I would check the battery contact points on the laptop, maybe one is bent or broken or dirty.

 

[alphaa10]

utroz-- Good guess, but on close inspection, no apparent problem with connector pin assembly-- all pins are straight and clean.

 

[ffg7]

part of power circuitry of motherboard is done it, might be a domed capacitor but I don't know.

 

[utroz]

As said above, it is quite possible part of the charging/Battery circuitry on the mobo is fried. You would need a real pro to take it apart to test things and even then it might cost more than the laptop is worth to fix. I could see one of the batteries being bad but both is very unlikely. Any chance you can test them in a different laptop that uses the same battery?

 

[alphaa10]

As said above, it is quite possible part of the charging/Battery circuitry on the mobo is fried. You would need a real pro to take it apart to test things and even then it might cost more than the laptop is worth to fix. I could see one of the batteries being bad but both is very unlikely. Any chance you can test them in a different laptop that uses the same battery?

All indicators now point to a problem with insufficient voltage at boot time, despite the new battery seeming to have a full charge. Of course, a full charge would not prevent some other factor from limiting sharply the available boot-time voltage. Below is a summary of what has been done, so far.
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Here is what I already have done to confirm a startup-phase battery voltage drop.

After pressing the start button with both power adapter and original battery connected, I allowed the laptop to proceed until it displayed the opening HP splash screen, then abruptly disconnected the power adapter plug. At that point, the laptop continued on its own battery power through the entire post, ending in a normal desktop display.

However, the revelations continued. After no more than 20 seconds, my well-used and probably weak original battery messaged that I should charge the battery, and the system quickly went into hibernation. I shut down completely and disconnected the power adapter.

Repeating the procedure for the newly-purchased battery, I first disconnected the original battery, and pressed the start button to bleed residual voltage. I substituted the new, "fully-charged" battery, and reconnected the power adapter. On pressing start once again, and after disconnection of the power adapter, the new battery sustained operations. I had enough time to open the on-screen battery meter and obtain a battery charge reading. And that reading was 100 percent!

To test whether the reading were false, I allowed the session to continue so I could observe whether the nominally 100 percent battery seemed fully charged. And to accelerate battery depletion by application of a modest load, I also ran an anti-virus scan of the entire system. After 20 minutes, my screen display of battery power reserve was still at 84 percent.

Now, the conclusion is inescapable-- the system has a point of resistance somewhere that sharply limits available startup current. The charging circuit itself seems normal, since otherwise, the new battery would not have performed as well under load as it did.

Somewhat unfamiliar with the various board components of the typical laptop, I must determine where the problem lies. Yes, it could be simply a bad connection, and I certainly hope for that. But it might be a circuit board, and the cost of even used 2125 mainboards is so prohibitive, I reach the point of having to analyze cost-effectiveness of repair.

I have tried to examine the voltage of the CMOS battery, but there are no exposed leads to contact with meter probes. I did disconnect the battery, however, in order to reset CMOS to default values, then reset all original values.

In earlier comments from elsewhere, it was suggested a weak CMOS battery might not permit proper loading of certain drivers, including the driver for battery condition and/or management of the charging operation.

 

[ffg7]

cmos battery is usually 3 volts.