Saturday 3 March 2012

Dell 1525 battery not charging

My wife's Dell 1525 Ubuntu laptop starting having battery problems last year and eventually we ended up with a totally dead Li-ion battery.   Fortunately I was able to acquire a clone replacement for about £25 which charged fine and worked for a week before becoming totally drained.

According to some users, this happens because the charging circuitry has died, which was a little alarming since the machine was way out of warranty.  So I had a machine that runs fine on AC power, but the battery won't charge.   So I slept on the problem and this morning I thought I'd try another spare Dell AC adapter just to factor out the AC power supply.  To my surprise the battery started charging, so I had to conclude the problem is simply due to a broken AC power supply.

So if the AC power supply is not charging, perhaps the original battery wasn't dead after all.  I plugged in the old battery, gave it an hour to charge but found it really was dead and useless.

I've compared the characteristics of the working power supply against the broken one with a multimeter and I cannot see any difference, which strikes me a little curious.   If anyone has any ideas why one works and other other doesn't please let me know!


After a bit of research I found a relevant article at [1] that describes the AC adapter battery charging issue.   So it seems that this is a common issue [2]  for a bunch of AC adapters and the author suggests a possible design issue [3].




  1. What does the firmware menu tell you about the PSUs in both cases? The Dell PSU reports its output wattage to the laptop, and if the laptop doesn't think there's enough available it'll refuse to charge the battery.

    1. Matthew,

      The firmware reports:

      Working PSU: 65W
      Broken PSU: "Unknown device installed"

      Any idea how the firmware figure this out?

  2. I think this is a Dell thing, they have chips in their power supplies which identify them as genuine and how much power they can supply, if that chip (or its wire in the supply cord) is damaged, the charging circuitry is disabled (supposedly to prevent low wattage power adapters overheating) but the laptop is still provided with power from the power adapter.

    1. Sound totally plausible. I'd just like to find out how it works - it seems undocumented and proprietary which makes me really curious about the exact mechanism being used.

  3. Most likely the signalling between power supply and laptop has broken down. Quite a few vendors use "smart" power supplies nowadays - having some kind of computer<->power supply communication over the power cable (info on wattage and so on). If the computer cannot identify it, it will just refuse to use it for charging. Some also reduce the maximum speed of cpu/gpu. My guess would be that it is to limit the risk of burning out a power source it knows nothing about. And to make it harder for people selling 3rd party supplies of course ;-)

  4. I'm sure that lying around for one year in a deeply discharged state can kill a Li-Ion battery (even with smart battery monitoring circuits), but that doesn't explain the power supply story. Have you checked the notebook's power socket? Maybe the power connectors differ just slightly, making the new one "fix" the broken socket.

  5. Just off the top of my head, I wonder if the contact portion of the connectors are exactly the same length? It is possible that one is slightly longer or the inside contact of the plug is slightly enlarged, thus making poor contact.

    1. Charlie, I've checked the connectors and they look OK.

  6. I had this on a colleagues Dell Laptop whose battery was dead. Bought him new battery and it worked but would not charge. He also had a dodgy socket (wire had tape arond it!) so I got him to buy another one and it worked not only much better BUT also started to recharge his battery. Additional bonus was that having decent power in also made his cdrom come alive again.

    One happy customer

  7. Richard Mortimer3 March 2012 at 22:38

    I had exactly the same problem with my Inspiron 1525 earlier this week. Same symptoms with it saying the PSU was an unknown device. I replaced the PSU and all is fine.

    Interestingly the old PSU would sometimes charge so I'm guessing that the "smarts" were just giving in the ghost.

  8. The power cord between the PSU and the laptop has 3 wires.
    The middle one is a very fine one and it is used for chargind the battery.
    When that one is broke the laptop works just fine connected to the power source but would not charge.
    This is what actually happened to me on a DELL A860.

  9. This issue on the inspiron 1525 and 1526 is actually usually caused by a failure of the DC Jack Board. If this is not the case, it's possible there is an issue with the 1-wire communication systm (I.E Severed connection inside of A/C adapter, dead DS2501 IC in A/C Adapter, or failed Mosfet on the system board)

  10. Cool! I never thought that a laptop battery problem can be managed with the ‘sleep on it’ tactic. :) Although the problem I had was with the charger itself. I found my lab chewing on it! >.< I’m just soo lucky that the battery still has 90% of its power. And that lasted for 4 days. :D That was a Dell 1525 too, btw?

  11. It depends on your power settings in the bios. On the older Precisions I've had them setup to use full power and they

    refused to even recognize a 65W adapter was plugged in until you turn on all kinds of power saving and throttling options.

    However once you shut them down they will charge just fine off a 65W adapter.

    There's more to this than 65W vs. 90W. If that had been the only difference, you would not be having a problem. In

    selecting a charger unit, you need to make sure several items match up:
    1. Is the charger unit supplying AC or DC to the laptop? MUST be same as specified for the original charger.
    2. Type of battery in the laptop. Many chargers are designed for a particular battery type and supply exactly the right

    voltage and charging rate (current) for that. Some even are "programmed" to alter the charging rate depending on the state

    of the battery's charge. All have a limit on the battery's maximum voltage to avoid over-charging. All of these are

    important, and that's why using the wrong charger can cause trouble.
    3. Polarity of the connector - MUST be the same as original.
    4. Voltage MUST be the same.
    5. Wattage MUST be at least as much as the original charger, can be higher without problems.
    6. Max amps must be at least as much as the original, can be higher.
    7. Connector on the end of the charger cord - must be the same size pins and spacing so that it fits the connector in your

    laptop without damaging it.
    For more: