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wondering about battery charge failure on T25 (or T430)...

T430-T490, T530-T590 Series
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lalisa
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Joined: Thu Feb 24, 2022 9:48 pm
Location: Brooklyn, NY

wondering about battery charge failure on T25 (or T430)...

#1 Post by lalisa » Thu Feb 24, 2022 10:21 pm

Hi,

I'm new here, will be very grateful for any pointers. I have a Thinkpad 25 anniv, very lightly used to the point that it works fine on either external 20V and USB-C power but I had not noticed it does not charge the batteries. And now it's well out of warranty. Both internal and external batteries are same, they were both original from factory, I've tried changing them over to new (cheap 3rd party or reconditioned lenovo) ones, at least one of which discharged fine but then behave the same, do not recharge.

At least while running Linux, if I connect either battery while the power is on, I do see minimal SMBUS information, manufacturer and so on, but no voltage or charge or charging reported. Under Windows I just get grumbling that the batteries "are not detected" and zeroes in all the battery info.

So I followed along with a couple of youtube videos, traced along much of the motherboard power circuit looking at least for shorts or failed components or obvious physical oddities, I found a T430 schematic online which helps understand the board a little, though can't see anything immediately wrong. And everything seems just fine under external power, there are no components looking like they were very hot or smoking.

In a simpler world I might have concluded that the charger IC had failed. But in parallel I'd been reading about Thinkpad battery whitelists etc and realizing just how much trouble the EC can cause, perhaps the machine is just sulking. However at this point the schematic starts to get a bit intimidating, I don't know yet how the EC logic integrates into the charging circuit.

What I'd appreciate pointers on is the best direction to continue looking:
- should I expect to see a nice charging voltage being presented to the battery derived from the AC power, and if I don't it's because there is likely a physical component failure somewhere along the way?
- or alternatively, is it likely that the circuitry could be just fine but the EC is somehow cutting the charging power, e.g. maybe the original batteries was seen as totally dead, and the replacement batteries are seen as fake, or computrace thinks the laptop is stolen, or any other manner of logical nonsense?

How do I narrow down where to look further?

Thanks for any suggestions or encouragement or moral support!

RealBlackStuff
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Re: wondering about battery charge failure on T25 (or T430)...

#2 Post by RealBlackStuff » Fri Feb 25, 2022 2:33 am

Welcome to the Forum.
Instead of that T430 one, get the proper T470/T25 schematics here.
It's called CT470 NM-A931.pdf there and you need to register (free) before you can D/L it.
Did you check the fuses in the charging circuits?
Are you using a dock?
If so, check this: viewtopic.php?t=128128

The batteries are about 5 years old by now, they may be on their last legs (or dead).
These ThinkPads can all use the same batteries: T470, T480, T570 T580, A475, A485, TP25, P51S, P52S
Replacements e.g. here: https://www.amazon.com/Lenovo-T470-Batt ... n%3A720576

FYI: only the T430/T530/W530/X230 had that EC battery check.
Lovely day for a Guinness! (The Real Black Stuff)
Lenovo: X240, X250, T440p, T480, M900 Tiny.

PS: the old Boardroom website is still available on the Wayback Machine
.

lalisa
Posts: 2
Joined: Thu Feb 24, 2022 9:48 pm
Location: Brooklyn, NY

Re: wondering about battery charge failure on T25 (or T430)...

#3 Post by lalisa » Sat Feb 26, 2022 6:48 pm

RBS - thank you so much, that's really helpful information and encouragement.

Having the right schematic is a big help! I'm not using a dock. Yes, I think I've checked a lot of fuses, though it seems most of those are for power input; the output path to the battery doesn't seem to have one - it's just a mosfet gated from the driver pin of the BQ25700 charger chip and then a shunt resistor. I think, anyway.... I should look more carefully.

Appreciate the note about the genuine battery check, hopefully Lenovo saw the error of their ways. And you're perhaps indeed right that just buying the proper batteries might be the simplest idea, though I don't like abandoning the old ones without knowing that they're really dead. I wonder how hard it is to build a stand-alone battery charger? Maybe one can make a raspberry pi or an arduino speak SMBUS protocol with the battery. After that it's just a bit of voltage, right? Perhaps with a current limiter and thermistor monitoring to be safe.

RealBlackStuff
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Re: wondering about battery charge failure on T25 (or T430)...

#4 Post by RealBlackStuff » Sun Feb 27, 2022 3:19 am

For the batteries you need to check fuses PF3 and PF4 near the battery connectors.

You can get a Lenovo external battery charger 40Y7625 e.g. here.
They can charge any (external) battery from T60 up till and including Tx70/T25 Series.
From Tx80 the battery connector may have changed.
Haven't seen one, so can't confirm (but is irrelevant here).

Make a battery extension cable as seen here.
Using the female connector from a dead battery (or the T60 interposer), and the male internal battery socket from a dead xx40-xx70 mobo you should also be able to concoct a battery extension cable for the internal battery.
From what I can see, these small sockets only have 2 flat pins, so you could make your own flattened nails or something.

Anyway, I'm no electronics guy, so don't know really how to test a battery charging circuit.

Check around if anybody has an xx40/xx50/xx60/xx70 or T25, then try your batteries in there.
Lovely day for a Guinness! (The Real Black Stuff)
Lenovo: X240, X250, T440p, T480, M900 Tiny.

PS: the old Boardroom website is still available on the Wayback Machine
.

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