If you want to use CR2032 battery you'll need a diode to prevent the board from trying to recharge the battery.

Or you can get these https://www.ebay.fr/itm/Super-Farad-Capacitor … N2Frezquxz0fbsw

They work pretty well and are drop in replacement (as long as you manage to solder both end to the moterboard obviously)

🤣 I just bought a pack of ten of those CR2032 holders in the hopes of replacing a 2032 battery.
Hopefully a rechargeable won't need the diode?

Hamby wrote:

🤣 I just bought a pack of ten of those CR2032 holders in the hopes of replacing a 2032 battery.
Hopefully a rechargeable won't need the diode?

Lithium rechargeable cells are quite different to the original NiCd or NiMH cells included in most older boards. They have a very different charging profile and are more volatile if charged improperly. Feel free to do as you wish, but understand using them for an application where they weren't intended entails some risk.

If you have an external battery jack on your motherboard, why not try inserting a 10k resistor to test. If the circuit is non-rechargeable safe, you should see no voltage drop across the resistor (full drop across the blocking diode).

Deksor wrote:

If you want to use CR2032 battery you'll need a diode to prevent the board from trying to recharge the battery.

Or you can get these https://www.ebay.fr/itm/Super-Farad-Capacitor … N2Frezquxz0fbsw

They work pretty well and are drop in replacement (as long as you manage to solder both end to the moterboard obviously)

This is an interesting alternative. Do you know how long a super cap will keep the clock functioning and CMOS data intact? And could they be put in parallel for super duper capacitance?

Didn't you already do this thread? 486 Dallas battery coin adapter mod ?

Google is such a nice tool sometimes 😀

Charging resistor needs to be removed (100...470ohm) from the charging circuit, once that is done there are no problems with installing a lithium cell or any other non-rechargeable cell in the machine.

Thanks guy's, You gave me some solutions and options.

Intel486dx33 wrote:

Thanks guy's, You gave me some solutions and options.

Again.

Tiido wrote:

Charging resistor needs to be removed (100...470ohm) from the charging circuit, once that is done there are no problems with installing a lithium cell or any other non-rechargeable cell in the machine.

But then you're running the RTC from the battery 100% of the time, yes? The charging circuit also seems to be the power supply for the RTC while the system is powered on. At least on my boards.

On all my boards 5V takes over when power is applied so battery is never left on 100% of the time, only charging of battery gets disabled (battery remains at its voltage). I haven't had battery ran out on any of the boards yet either.

Hm, both of my 486 boards powered the RTC through the charging resistor. They have discrete crystal + feedback amp circuits for the oscillator near the battery area, but I suppose that could have been back-fed aux power through the trace that went from the battery to the RTC, which is integrated into the chipset. I hadn't checked that.

I just used an old phone battery and a cable with a plug from amazon

https://www.amazon.com/gp/product/B07MC2CSQ1/ … 0?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B07NWD5NTN/ … 1?ie=UTF8&psc=1

same voltage, same rechargeable chemistry etc, but not on the board and removable and replaceable if I put it in storage.

gdjacobs wrote:

Lithium rechargeable cells are quite different to the original NiCd or NiMH cells included in most older boards. They have a very different charging profile and are more volatile if charged improperly. Feel free to do as you wish, but understand using them for an application where they weren't intended entails some risk.

What exactly are the risks? Through the years, I have used a rechargeable lithium on some of my boards. They work as such, and they never get warm. That said, I never turn on a vintage computer, more than some 2 hours.

The type I use, are this one.

I can see it would pose a potential risk, if I have the computer turned on for an 48 hour gaming session, yet I am too old to go that long without sleep, and I dont know anyone in real life that are interrested in an old school gaming/computer weekend, like the ones I attended before networking was a thing to have on a computer in private. (Between 1988 and 1992).

Right now, I only have one computer left, that has such a battery I linked to. And I soldered it on the motherboard around 6 to 8 months ago. Still works, never gets warm and I have only used the machine a couple of times and no more than 30 minutes each time.

External battery holder with 4 AA rechargable batteries or 3 AA non-rechargable batteries (use only if you are sure motherboard is not chargin through external battery port!).

OR

Supercapacitor

OR

Barrel battery mounted externally connected to external battery header (ideally mounted in some sort of enclosure).

Option 1 and 3 is how it was done in the past so is ideal, era-correct solution. Option 3 is elegant (there are some supercaps that look like a barrel battery). Electrohacker's solution is very good as well!

Personally I wouldn't use coin cell with diode.

Well the connector is like that for a NON-rechargeable battery. I assume the replacement might have been a Rayovac 4.5v alkaline computer clock battery.

So I think a 3 AAA battery holder should work with standard non-rechargeable AAA batteries.
or
A regular CR-2032 coin battery with holder should work.

brostenen wrote:

What exactly are the risks? Through the years, I have used a rechargeable lithium on some of my boards. They work as such, and they never get warm. That said, I never turn on a vintage computer, more than some 2 hours.

Worst case, exothermic reaction and fire.
https://www.aiche.org/sites/default/files/doc … onBatteries.pdf
https://www.researchgate.net/publication/3219 … er_Overcharging

Here's a recent setup I did on a 386SX: External battery header to a 3xAA battery holder; I use rechargeable AA batteries but recharge them externally when needed.

Intel486dx33 wrote:

Well the connector is like that for a NON-rechargeable battery

Are you sure?

Many motherboards will charge the battery hooked up to external battery connector. It was never standarized.