T520: Slice battery charging thresholds stuck

Question

I bought a T520 (4240) a few months ago and, like most people around here had the same issues with pulsing fans and, on applying BIOS 1.28, CPU throttling issues. I'm not sure if the latter one is fixed properly yet, but I also have a problem with the battery charging thresholds that has me stumped.
I have the 55++ and 27++ 9-cell main and "slice" batteries. For a while I let them charge up to 100% whenever connected to AC, but then I read that a 100% charge level is not recommended for day-to-day operation.
I use Fedora 15 Linux 99.9% of the time on my T520. I wanted to set the battery charge thresholds to avoid the 100% charge level, but the "tp_smapi" Linux driver doesn't work for the T520 (yet). I read somewhere that if I were to set the charge thresholds with the Lenovo Power Manager in Windows 7, that they would work in Linux as long as the laptop was not completely powered down when switching from Windows to Linux (i.e., use a warm boot). Well, it worked. In fact it worked really well: I could even power down and remove the batteries and something, somewhere would still remember that I wanted to start charging the slice battery when it dropped below 35% and stop charging it at 80%, even when running Fedora 15.
Having used the machine for a few weeks, I found that I used it on battery power a lot and liked to "top up" the batteries over night. The 35/80 thresholds didn't really suit my working pattern. So, back in the Power Manageer in Windows, I changed the battery thresholds from 35/80 to 50/88 for both batteries (55++ and 27++). On booting back to Linux, I noted that the main battery would respect the new levels, but he slice battery was still stuck on 35/80. Back in Windows, I tried changing the levels in different ways, but the slice battery refused to charge to more than 80%, even under Windows, no matter what I did. It seems that my first change from the default (is it 96/100?) to 35/80 has gotten stuck somewhere and I cannot change it again.
I even notice in the Power Manager that the slice battery constantly toggles between charging and not charging when under AC power if I set the threshold to 85/90. Because the 80% level where the battery is stuck is lower than 85% (my new "start" threshold), charging kicks in, but it immediately stops again, as it won't go over 80%, then, of course, it starts again and stops again, and so on.
How do I fully reset the charge thresholds on the slice battery so I can exceed 80% charge?

Answer 1

I had kind of given up on this, but thank you KooMaster for your confirmation that I am not alone with this issue. I don't think this is a problem with the Lenovo or Windows software, as this happens to me when running Linux without either of those. My guess is that the problem is in the embedded controller (EC) firmware. It is responsible for charging the batteries and enforcing the charging thresholds (that's why they still work even when the machine is turned off).
It probably makes sense to charge each battery to 80% first, as it likely only takes half of the overall charge time to get to that level (the last 20% taking as long again). That way, we get both batteries to a useful charge level as fast as possible. However, based on your observations, it seems that someone in Lenovo forgot to tell the EC to check that the main battery has reached its upper charge threshold, not that it has reached 100%, before topping the slice battery up to its upper charging threshold.
Can someone in Lenovo please comment on this issue, as I raised it over seven months ago now and I haven't heard a single word from any of you about it? "KooMaster" has confirmed the problem on a different model with different batteries, so it seems highly likely that a quick check of the (shared?) EC firmware code and a patch will resolve this quite quickly.
(I updated my BIOS and EC firmware today and it made no difference to my problem.)