Ultrabay Battery -- Change discharge behavior?

[andrewfong]

I have a T400 with the optional ultrabay battery. The behavior seems to be that the extra battery is discharged entirely before moving on to the main battery. My understanding is that completely discharging a Li-Ion battery shortens the battery's lifespan. It seems to make more sense to either (1) drain the main battery first since it's larger and less likely to completely discharge before you find a power outlet or (2) alternate between the two batteries.

Is there anyway to adjust the battery settings to achieve either of these?

[JaneL]

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andrewfong wrote:

Is there anyway to adjust the battery settings to achieve either of these?

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Nope, not that I've ever heard of.

[t61_owner]

Lenovo should at least give us the option to specify a threshold so as to not drain the batteries to zero.

Message Edited by t61_owner on 03-15-2009 09:33 PM

[stadi]

Hi all,

I think, you missunderstand these 0% of battery charge. This does not mean, that the battery is discharged to 0 Volts. In that case, the battery would be destroyed immediately. These 0% are with respect to a minimum threshold voltage, such that the battery will not be damaged or its lifetime drastically reduced. When I have a look at my "fully" discharged ultrabay battery, I see that it has still more then 11V, which is no problem. The battery has 3 cells, each with 3.6 Volts. And a Li-Po Cell (Li-Ion is similar) can be discharged to about 2.8V without being damaged. 3 x 2.8V = 8.4V V for the whole battery. 11V is far avay from that, so there is enough reserve. If the voltage falls under a certain voltage, the computer turns off but not just because there is not enough power. Instead this is a safety mechanism for the battery which is implemented in hardware. So I think it's not necessary to wory about the battery.

Even though I think, that the user should be able to decide which battery discharges first. Especially if lenovo writes:

"Since the battery works in the Ultrabay you don't have to suspend the system to swap out the system battery to use the ThinkPad for an extended period of time."

That's what I wanted to do, change the main battery, while the system is on. But with this default behaviour of battery management, it's impossible because the U-battery is discharged first. Escept you carry the U-battery seperately with you the whole day and insert it shortly before the main battery is empty. But that's not very comfortable.

I foud one way to achieve that the main battery is discharged first. I have a T400 and if you apply the small switch on the right if as you wanted to remove the battery and the pad to pull jumps out, then the main battery is discharging while the ultrabay battery is still connected (appears in the Power manager) and supplies the PC with power if the main battery gets empty. But also that is not very elegant.

I hope I helped a little. If someone has a real solution to this problem, please tell us. I know that there is a solution, even if not supported by lenovo, what is a shame. (Something with ACPI events I guess but I don't have experience with that)

[t61_owner]

It's not the voltage that you should be looking at to gauge the capacity of your battery.  It's the watt hour (wh).

And when the indicator is at 0%, the battery is FULLY discharged.  There is no "reserve".

[stadi]

Sorry, but you are wrong. I'm an electrical engineer, I know what I'm talking about. What you call capacity (Wh) (by the way this is the energy in the battery). Capacity is a bad word in this context anyway. Cpacitors have a capacity but not batteries. Anyway, the capacity the Power Manager shows is just an estimate an it is with respect to what you can take out of the battery without damage and NOT the absolute Energy remeining in the battery. There is still a lot of energy in it, when it shows 0 Wh. You can plug a lamp to the battery and it will burn. As I said, if you would really discharge the battery under about 8.4 V it will damage immediately, it will inflate because of gas creation inside and can not be used anymore (bad behaviour of Lithium batteries).

The only quantities you can measure is voltage and current. And your Notebook will turn off under a certain voltage to protect the battery.

THAT'S HOW IT IS!

[stadi]

By the way, try it out. Disable automatic shut down or hibernation by software, let your notebook on and observe the Energy remaining (Wh) in Power manager. The notebook will still run when it shows 0Wh and there is still a current (of course). Then observe the voltage: It will fall to a certain value till the notebook turns off.

Note that this may not work with all batteries, for some the notebook will turn off before 0Wh are reached because of differences in descharge-voltage curve. And it will also not damage the battery.

[t61_owner]

Of course you're an electrical engineer...

When it goes to zero, it's zero.  Otherwise, why worry about battery lifespan if you can't ever drain completely?  I've been through 2 ultrabay batteries that have lost over 70% of its capacity within a few months, using the SAME main battery that still has 95% of its capacity.

If your laptop is operating after your battery reaches zero WH, then your laptop/battery is reporting incorrectly.

[stadi]

In fact I got an old X41 battery that had about 60% of the capacity. With regular charging and discharging (more than 0% until the machine turned off) I got it back to 80%.

I know Lithium batteries also in other contexts (not only notebooks or other electronics devices) and there is nothing wrong to discharge them to their nominal voltage of 10.8V. Which does not mean that it is completely empty.

The loss of capacity of your batteries has other reasons and there are many many of them. In my case, the main battery is a Li-Ion and the ultrabay a Li-Po battery which means that they have a different origin what could be the reason of quality differences. Another example is keeping the battery mostly or fully discharged and not use it for days, weeks or even months. This is very bad for the battery. Or charging the battery to 100% is a much stronger torture for the battery than to discharge it to 0%. So if you want to  protect your batteries, use the option in the Power manager to limit the maximum charging.

If you don't believe me, just ignore it. I'm sure you'll find some other noobs that shares your opinion.

[t61_owner]

While it's true charging a battery to 100% is bad, my experience is that draining a battery to zero is just as bad.  These batteries should not be deep-cycled frequently nor taken below a minium voltage (per cell).

If you're really an electrical engineer, you should know this.  And yes, I will ignore you.