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701C replacement batteries

Older ThinkPads.. from the 600, the 7xx, the iSeries, 300, 500, the Transnote and, of course, the 701
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MooNWalker
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701C replacement batteries

#1 Post by MooNWalker » Sun Jan 06, 2019 1:08 am

Yes, plural - this machine has three of them: the main NiMH battery, the standby backup battery (Varta V30H NiMH cell), and the CMOS battery (so far haven't been able to identify).

In the unit I'm trying to restore the main battery leaked, the standby backup battery is suspected to have been damaged (may have leaked itself, though it also could be dried electrolite from main battery leak), CMOS battery is dead. I do have an original main battery replacement, so that is not a concern. My concern is first and foremost CMOS battery, and then the standby backup battery.

I'm still waiting for the soldering iron to arrive to be able to desolder the CMOS battery from the motherboard (it's soldered on the lower side of the bottom planar next to the IDE connector and the RAM slot) and hopefully identify it, but I'd appreciate any info on what is it, what are its specs, and what it can be replaced with. This thread seems to make a claim that a cell used in more modern ThinkPads (apparently a CR2025 type Lithium cell) will be safe to use in 701C, how certain is that? IIRC CR20xx type Lithium cells aren't really rechargeable (are they?), so the main concern would be to make sure that a) the voltage is correct (should be exactly the same across the same type/chemistry) and b) it can output the current it needs to output and still last long enough (hopefully at least few years before I have to re-solder it again). Is my thinking correct?

I already know what kind of battery is the standby backup one, but I can't find the exact replacement. This one is obviously rechargeable, how important is it to match capacity, is it OK for replacement to be of higher? Are there any other parameters I should worry about besides matching chemistry and perhaps current/capacity? What about internal resistance?

It's been a veeeeery long time since I've done anything related to electrical engineering...
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MooNWalker
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Re: 701C replacement batteries

#2 Post by MooNWalker » Sun Jan 06, 2019 1:58 am

I get it that many modern CR button/coin cells (CR - IEC code for cell based on Lithium chemistry) can last many years... But I wonder if an ML1220 cell would be a better fit for the CMOS battery in 701C?
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RealBlackStuff
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Re: 701C replacement batteries

#3 Post by RealBlackStuff » Sun Jan 06, 2019 8:42 am

No, won't work, there's no 'power' going into the battery to recharge it.

On the 701c I worked on, the CMOS was not soldered, but had a socket.
CMOS see here: viewtopic.php?p=828410#p828410
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MooNWalker
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Joined: Sat Mar 22, 2008 6:54 am
Location: Seattle, WA

Re: 701C replacement batteries

#4 Post by MooNWalker » Sun Jan 06, 2019 1:31 pm

RealBlackStuff wrote:
Sun Jan 06, 2019 8:42 am
No, won't work, there's no 'power' going into the battery to recharge it.

On the 701c I worked on, the CMOS was not soldered, but had a socket.
CMOS see here: viewtopic.php?p=828410#p828410
I think you're right - I haven't yet been able to remove the solder tabs from the original CMOS cell, but from what I can make out behind them it's a BR1225, which is not a rechargeable type, so it's probably indeed safe to just replace it with something like CR2025/CR2032 used in more modern ThinkPads, though I can't find one with matching solder tabs.

For the standby backup battery I think I found a replacement. It's not an exact model, Varta V30H, as those appear to have been discontinued, but Varta V40H appears to be intended as a replacement for V30H, so I should be able to use that one - just put the existing wires onto new cell's solder tabs, matching the polarity, and then put some heat shrink tubing around it to prevent shorts.
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hjanzen
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Re: 701C replacement batteries

#5 Post by hjanzen » Fri Jan 11, 2019 12:56 pm

600X PIII 650MHz 576MB, 701C DX4 75MHz 40MB, T61

hjanzen
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Re: 701C replacement batteries

#6 Post by hjanzen » Fri Jan 11, 2019 1:04 pm

Cmos battery replacement

Or you may have a look here:

https://thinkpad-forum.de/threads/16163 ... ans+janzen
600X PIII 650MHz 576MB, 701C DX4 75MHz 40MB, T61

Thinkpad4by3
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Re: 701C replacement batteries

#7 Post by Thinkpad4by3 » Fri Jan 11, 2019 1:18 pm

hjanzen wrote:
Fri Jan 11, 2019 12:56 pm
https://www.mupload.nl/img/81gr7xx0fclav.jpg

Cmos battery replacement
Remove the tags the picture is WAY WAY TOO BIG!!
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The efficiency of two screens equally sized with equal numbers if pixels are equal. The time spent by a 4:3 user complaining about 16:9 is proportional to the inefficiency working with a 16:9 display, therefore the amount of useful work extracted is equal.

hjanzen
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Re: 701C replacement batteries

#8 Post by hjanzen » Fri Jan 11, 2019 2:02 pm

For the standby backup battery I have used a Panasonic VL1220-1VCE
600X PIII 650MHz 576MB, 701C DX4 75MHz 40MB, T61

MooNWalker
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Re: 701C replacement batteries

#9 Post by MooNWalker » Mon Jan 14, 2019 8:40 pm

I ended up using CR2032 cell for CMOS battery. Was a bit tricky to fit it next to the speaker, but works beautifully now otherwise. For the standby battery I found Varta V40H with solder tabs.

Thanks everyone!
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