Thinkpad battery won't charge fully

October 24, 2006 7:29 AM

Why won't my Thinkpad battery charge fully when it's plugged into the wall?

I have a 2-year-old Thinkpad T42, which I essentially never unplug from the wall socket. For the past few weeks, the battery power indicator has been hovering at about 75%, instead of 100% as previously. The computer's working fine -- but is there something wrong with the power supply that's going to make it die in the near future? Do I need to buy a new battery? Or is this a non-problem that I can ignore?

posted by escabeche to computers & internet (10 comments total)

Could be a worn-out battery. Older thinkpads used to totally kill batteries if they were left plugged in all the time (google for thinkpad 600 problems). This doesn't happen anymore, but batteries are consumables and will wear out, some more quickly than others. It happens with all laptops eventually.

It's a non-problem as long as you don't mind having a battery with a shorter runtime. If you never unplug it, you may want to remove the battery, which will probably prevent the problem for getting any worse.
posted by GuyZero at 7:45 AM on October 24, 2006

There's two separate problems here: One is that the charging thing only gets to 75%, and the other thing is that your battery discharges faster than it did when it was new.

You could probably solve the "75%" problem by cycling the battery a few times to make the computer learn about its new, shorter capacity: discharge it all the way, charge it up all the way, and repeat a few times. That should make it read 100% when it's fully charged. You may have to disable Windows' power-saving functions or even power controls in the BIOS to prevent the laptop from shutting down at 5% remaining power; to recondition the battery you really need to drain it fully.

What it doesn't do is actually let the battery last longer. If you need the battery life, and not just a 100% reading, then you need a new battery. Two years is pretty much service life for a laptop battery.
posted by mendel at 7:48 AM on October 24, 2006

If your batteries are Lithium Ion, they have a finite life and will degrade sharply after a year or two of use. They will do this even if left unused on the shelf. You may have reached this point. Buying a new LiIon replacement may solve your problem.
posted by fake at 7:53 AM on October 24, 2006

"Why won't my Thinkpad battery charge fully when it's plugged into the wall?"

I'll tell you why:

"I essentially never unplug from the wall socket."

That's why. Your battery is shot due to having been overcharged for two years straight. You'll be buying a new battery to fix this problem, and then hopefully not leaving it to cook for years at a time.
posted by majick at 8:17 AM on October 24, 2006

Great answers, all, thanks. So, majick, is the right approach to put the battery in only when I'm going to use the laptop away from the wall?
posted by escabeche at 8:46 AM on October 24, 2006

FWIW, I do the same thing (keep a thinkpad plugged in all the time, and I almost never turn it off). I've got a T40, it's about three years old, and the battery info is:

present: yes
design capacity: 47520 mWh
last full capacity: 28170 mWh
battery technology: rechargeable
design voltage: 10800 mV
design capacity warning: 1408 mWh
design capacity low: 200 mWh
capacity granularity 1: 1 mWh
capacity granularity 2: 1 mWh
model number: IBM-08K8193
serial number: 1234
battery type: LION
OEM info: SANYO

So, over the course of three years, it's gone from holding 47520 mWh to only 28170 mWh. The laptop runs linux; this info is from /proc/acpi/battery/BAT0/info. I have no idea how you'd get the equivalent on Windows, although there's probably an ACPI dingus somewhere that will do it.

I leave the battery in on purpose as it (a) gives me the greatest ease of use, and (b) acts as a built-in UPS (if the power goes out, my laptop doesn't die). I rarely use it on battery only. I also don't own the laptop; it belongs to my employer.

If memory serves, the standard battery is not hot swappable, but there is a battery available for the ultrabay (the bay that usually has a CD or DVD drive) that can be hot swapped.
posted by doorsnake at 10:28 AM on October 24, 2006

If you want you can install the battery maximiser on your Thinkpad.

It will check the health of your battery and it also gives step by step instructions on how to recondition the battery. If the battery health is poor you're probably better off getting a replacement but since you always use AC power it might not be worth it.
posted by mgrimm at 11:35 AM on October 24, 2006

I also have a two year old T42 that I almost always use plugged in. I had exactly the same problem a couple of months ago. I used the battery and ran it down all the way a couple of times. The problem seemed to resolve itself.

I also have a TP 770ED which I always used with AC power and the battery in. This was a problem. I eventually killed the battery. When I got the new TP I was concerned about the battery issue, but I read somewhere that this was no longer a problem with the TP batteries. I do unplug my TP when it is not on.
posted by noether at 3:42 PM on October 24, 2006

Many notebooks have a "Recalibrate" option for the battery - check your manual or the website. You'll have to leave it run overnight (well, at least in my experience, you can't do anything else while it recalibrates).
posted by IndigoRain at 6:15 PM on October 24, 2006

As of last night, the screen started suddenly going dark about 5 minutes after startup (still plugged in to the wall.) At first I could get the screen to light up again by closing and opening the case, but then that stopped working too. The computer's obviously functioning (I can hear the drive whirr) but no screen. I think it's time to have somebody look at it in person...
posted by escabeche at 7:50 AM on October 25, 2006