SirNickity wrote:

I really can't understand why people still do this hack. They still manufacture drop-in replacements, and there are no shortage of DIY boards to adapt the equivalent external-battery package to that integrated-battery PDIP form factor. Why go to the trouble of mutilating a dead one when there are so many better options readily available? It doesn't make any sense.

Because I have a dremel, a bunch of coin cells, several coin holders, and soldering gear aplenty, and this have job is like 30-40 minutes of work and costs me pennies, whereas a new RTC chip would cost me $20 plus shipping time, and mine are much prettier than the pic I posted.

I also feel like a battery I can't see is an acid hazard waiting to happen, and I have nightmares of CPS2 arcade boards ravaged by battery acid.

I guess I didn't expect so many people to have a stock of coin cell holders. I figure, if you have to order a part anyway, just do it right. To each their own, I guess, but it just makes the poor motherboard look like it got into a knife fight. 😉

DNSDies wrote:

I also feel like a battery I can't see is an acid hazard waiting to happen, and I have nightmares of CPS2 arcade boards ravaged by battery acid.

But it is really the opposite - an exposed battery is going to do damage if it leaks, one potted in plastic is not

artiemog wrote:

I've seen some rumours floating around that the replacements aren't 100% compatible with all designs that used the old chips, so […]
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SirNickity wrote:

I really can't understand why people still do this hack. They still manufacture drop-in replacements, and there are no shortage of DIY boards to adapt the equivalent external-battery package to that integrated-battery PDIP form factor. Why go to the trouble of mutilating a dead one when there are so many better options readily available? It doesn't make any sense.

I've seen some rumours floating around that the replacements aren't 100% compatible with all designs that used the old chips, so it may be paranoia. It also seems like a lot of people just aren't aware that the new chips exist, but information about the hack has circulated around a lot.

I found the replacement chip to be an excellent solution though. I got a DS12887+, which is Maxim's current replacement for the DS1287, and installed it on a 486SC-P Rev. D2 motherboard yesterday (along with a socket! Curse this cheap motherboard manufacturer for not socketing a chip with a battery inside...). Worked like a charm, first try. I will admit to being very careful while removing the old chip in case it turned out I would have to perform the hack, though.

Old chip:

New chip installed on the motherboard:

Good work, you're doing it right

maxtherabbit wrote:

Good work, you're doing it right

Just in case you haven't gotten the message yet, there is no one "right" in this situation.

precaud wrote:

maxtherabbit wrote:

Good work, you're doing it right

Just in case you haven't gotten the message yet, there is no one "right" in this situation.

Hello.
Another question with few answers.
Was it a simple Li battery or a Li accu in the dallas?
I juste worked on a clone, a M48T86PCI , access is on the small side opposed to the pin1 point.
After liberating the two pins and cuting the (+) from the battery, I still get some voltage when the pc is running. So I prefered to put a 3.8v accumulator than a Li classic battery without any diode for security.
Does someone have some good informations ?

Sorry for the thread bump, I just figured this might be helpful.

I don't use debug often, so for whatever reason I was getting errors when I tried to just manually input the commands in the OP. I don't understand how. So, I instead copied it all to a stoprtc.txt file on a floppy, put it in an old PC and then ran the command: debug <stoprtc.txt

It seemed to work without errors but the system stopped responding at "-q". I did end up with a usable stoprtc.com program though. I tested it and it does seem to stop the RTC on my system! So, that's great.

One thing to note is that DOS does still seem to keep time while the system is powered after doing this. For example, I can zero out the clock to 12:00:00, run the command, count to 20 and DOS will say it is 12:00:20. DOS must be keeping track of time itself while it is running, even without the RTC keeping time. The program is actually working though because if you zero out the clock, run stoprtc, shut the system down, wait 20 seconds and turn it back on the clock will not have counted that 20 seconds.

Anyway, I've attached the working stoprtc.com program (in a zip) to this post so people can skip the debug part all together. Should save some time.

You perhaps may see the clock difference with CheckIt!

Ozzuneoj wrote on 2026-07-02, 21:21:

It seemed to work but froze at -q.

I'd have to test to confirm whether it's a valid concern, but possibly a final new-line after the q is required to finish the command.

Ozzuneoj wrote on 2026-07-02, 21:21:

One thing to note is that DOS does still seem to keep time while the system is powered after doing this. For example, I can zero out the clock to 12:00:00, run the command, count to 20 and DOS will say it is 12:00:20. DOS must be keeping track of time itself while it is running, even without the RTC keeping time.

The BIOS keeps track of the time of day using the timer interrupt IRQ0, and DOS knows the current date. DOS can use the time-of-day overflow flag provided by the BIOS to increment the date. This is completely independent of the RTC, which is used by DOS to initialize its date. I'm unsure whether the BIOS already initializes the time-of-day counter from the RTC before it boots an operating system. It is vital that this technique works without and RTC because PC/XT systems had the real-time clock as an optional 3rd-party add-on, but the DOS time and date was support to work once initialized after powering the system (and that's why DOS asks for time and date if you power up without autoexec.bat)

Ozzuneoj wrote on 2026-07-02, 21:21:

Anyway, I've attached the working file (in a zip) to this post so people can skip the debug part all together. Should save some time.

Thanks. When I made that original post, I wasn't aware that it is possible and allowed to post COM files inside of ZIP files, while COM files on itself are blocked.