http://www.powerstream.com/p/Lir2032.pdf

It will work as long as the voltage on the battery will not get higher than 4.2V.

Remove the battery and check what voltage is provided by the board. Also, you should remove the cell when the computer is not needed for a long time, as it takes damage when overdischarged.

Thanks for the reply!
The original NMh battery had 3.6V, so there should be no problem, right?

But what happens when the lithium battery is fully charged? NMh rechargeable batteries are known to be able to replace the old NaCd accumulators (the big blue ones, that often destroyed old 386/486 mainboards), but is the lithium cell also? Does the motherboard stop charging when the battery is full, or the battery itself?
By the way - the markings for the common coin cell holder on the pcb use exact the same connectors on the board as the original NMh battery.

The charging voltage is indeed the problem - it depends on the cirquit wether the charging voltage will be exceeded. LiIon cells turn into bombs if they are charged with a voltage too high. So

> Remove the battery and check what voltage is provided by the board.

The coin cell holder on the board is probably meant for a 3V non-rechargable Lithium battery. They'd have left out the charging cirquit if they had put that on the board.

Strange - I measured the voltage at the coin cell holder and got 4.65.V! To high it seems! The original NiMh accumulator has a nominal voltage of 3.6V (the lithium one 3.7V) On Vartas website I couldn't find informations about the charching voltage:
http://www.varta-microbattery.com/en/mb_data/ … ets/DS55602.PDF

(You have to multiply every value with three, as the cmos battery consists of three V15H, the sucessor of V11H)

I also measured the charging current at the coin cell holder, it was 1.95 mA, which is a little bit above the "trickle charging current" in the V15H data sheet and far below the values of the lithium cell. So what to do? It seems that the way of charging a lithium cell is very different from that of a NiMh accumulator.

The NI* cells are charged with constant current and unlimited voltage. The cell itself keeps the voltage low. The litium cell requires a limited voltage. It is possible that with a load the voltage will not rise as high as 4.65V but you'd have to check.

If this was my board I'd add another diode to the charging cirquit or disable it altogether and use a 3V non-rechargable lithium cell.

I don't know how accurate my understanding is, but I've heard that lithium ion batteries need nontrivial charging circuitry because there's a complex process that has to be done when they're near full charge.

First result on Google: http://www.batteryuniversity.com/partone-12.htm

It's really just limiting the voltage at the cell. With a regulated power supply: Set the voltage to 4.20V and the current to a value the cell can cope with (less current if it was discharged below a certain voltage level). And hope the supply doesn't break and put out more than that voltage.

Replacement Varta batteries can be had pretty easily. As a EE, I would not risk irreparably damaging retro hardware due to mismatched battery technology.

Go to www.digikey.com or www.mouser.com and search for Varta 3/V80H... That is a current Varta part number (shrunk wrapped triple cell pack) that is a drop in (or solder in) replacement for many of these old motherboards we have.

In fact, I've used them to replace the batteries in my IBM XT 5160 and my Packard Bell 286. No issues whatsoever.

So it gets another chance to ruin the board with acid...

Reviving this thread for a very important question 😀 - how can I tell if some barrel-type batteries that I have on a couple of old 486 VLB boards are rechargeable or not? It only writes "KTS 3KT60 3.6V60mAh 9411" on them (or "9412" - I assume it's the production year and week).

I'm planning to unsolder those and replace them with coin-like battery holders taken from defective modern boards (distance between pins differs by about 2mm, so the new ones should be pretty easy to solder in place), and I read here that 3V would do just as fine as 3.6V, but I don't want anything exploding in there...

There are also external battery connectors on the boards, but having the battery on-board looks more elegant to me 😀.

Thanks.

Yes, that battery is rechargeable. If you touch the battery contacts with a multimeter there's going to be a voltage. The best idea is to remove the old battery, and use the external battery connector, which is meant to be used with non rechargeables. If you still want to place the battery where the original was, you can do that using a diode. You can place that between the battery and the positive connector. That way it will prevent the battery from charging.

Bringing this up for some personal opinion based on my experience so far with barrel-type batteries... I've found two "types" of such batteries, that seem to differ in both aspect and functionality:

- I had three boards (2 * 486VLB and 1 * 486PCI) with leaking batteries; on two of them I soldered coin-type battery supports instead (I haven't found one for the third board yet) and they are running fine ever since (the coin batteries in place don't even get warm, so I don't expect them to explode soon)

- I also have three boards (2 * 386 and 1 * 486VLB) with barrel-type batteries that are not leaking yet, you can distinguish the word "CHARGE" stamped on one end and, most importantly, seem to be still alive & kicking (they retain BIOS settings over significant periods of time)

Is it possible that the first "type" is actually not rechargeable, while the second one is (which would explain their good shape over time)?

Isnt it just an idea to make an new topic which options you can use to replace the old battery?

does this item work with the external battery connector?

http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem& … em=260775151989

Probably, but it seems to me like it's nothing more than a 3x AA battery holder, with a speaker-like connector and cable attached to it. You can buy that from electronic stores for less than 2 euros.

ya, but I'm too lazy to search and visit one 😁