Having an unpopulated battery footprint on the PCB along with an external battery box is a period correct aesthetic

^good point.

Perhaps some small coin cells in shrink wrap?

I suppose an axial capacitor could be installed along with a external battery.

You can also use NiMh cells that are produced today

This would be period correct as well, but maybe a little bit less safe - we don´t know what these batteries look like in 30 years (personally I don´t care).

Maybe there is a way we can seal them or something.

majestyk wrote on 2022-11-18, 19:54:

You can also use NiMh cells that are produced today

varta2022.JPG

This would be period correct as well, but maybe a little bit less safe - we don´t know what these batteries look like in 30 years (personally I don´t care).

Are modern Nimh batteries lessprone to leaking? I guess we'll really find out in 15 years or so. It is very tempting to get one as they certainly look the part.

maxtherabbit wrote on 2022-11-18, 15:05:

Having an unpopulated battery footprint on the PCB along with an external battery box is a period correct aesthetic

Yes, I've seen that mentioned in many places. Still if possible my preference is to have "something" installed. My first PC was a slot1 machine so I don't know what was a common practice at a time of 386s, back then I could only browse magazines and dream of the time I'll be able to afford one 😀 , but I imagine huge majority of users back then simply used their built in battery (while it was still good).

When procuring stuff for my collection I have an emotional preference for "original" and unmodified(unless it was really done back in the day etc). Please note I'm not making a value judgement here I'm just describing my own personal preference.

It just so happenes out of the two 386 boards I have, one has what appears to be an original battery (with no leakage). The other had its battery removed. I'm very conscious of the need to replace those old bundles of acid just waiting to burst, but I would like to replace them with something that looks similar.

If not battery tech, then perhaps a dummy that hosts a capacitor. I did consider supercapacitors, but I read conflicting reports of the number of full charge/discharge cycles available and lifetime at zero charge.

Sphere478 wrote on 2022-11-18, 16:44:

^good point.

Perhaps some small coin cells in shrink wrap?

I suppose an axial capacitor could be installed along with a external battery.

If anyone knows the type/model number of a small rechargeable lithium cell sized like one of those 3 in a typical nickel battery please let me know. The remaining 2 could be just shells and the middle could be lithium if one of the right size exists.

If I recall, a lithium ion cell would fit the charge profile pretty closely. I’m pretty sure there are cells that are about that size (same as original nicad) but where the nicad was what 2 or 3 series, the lithium is 4.2v full charge with a single cell

Measure your voltage if it doesnn’t go below about 3.2 or above 4.2 a lithium ion would prob work. You could use a resistor to match internal resistance of nicad for voltage swing. As lithium holds voltage to charge level pretty strictly.

Anyway, you could solder leads to the ends or install a battery holder

https://www.digikey.com/en/products/detail/pa … ZhoC8LQQAvD_BwE

Does this size match?

Voltage seems to be 3.0v nominal. So I think this might be wrong one for you, but interesting none the less.

14240 might be the size. Those are mm in the model number. Does that match the original nicad? I’m not in front of one atm.

flynth wrote on 2022-11-19, 09:00:

Yes, I've seen that mentioned in many places. Still if possible my preference is to have "something" installed. My first PC was a slot1 machine so I don't know what was a common practice at a time of 386s, back then I could only browse magazines and dream of the time I'll be able to afford one 😀 , but I imagine huge majority of users back then simply used their built in battery (while it was still good).

what I meant is the systems didn't always even have the battery soldered to the board in the first place

flynth wrote on 2022-11-19, 09:00:

If anyone knows the type/model number of a small rechargeable lithium cell sized like one of those 3 in a typical nickel battery please let me know. The remaining 2 could be just shells and the middle could be lithium if one of the right size exists.

you CANNOT use rechargeable lithiums in place of the NiCd battery - lithium requires charging circuitry which these old boards simply don't have, and doing it anyway can result in a burst or incendiary cell

flynth wrote on 2022-11-19, 09:00:

Are modern Nimh batteries lessprone to leaking?

Haven't ever seen one do so (due to natural causes as opposed to overcharging, that is...) - but modern alkalines, especially reputable brands, tend to be worse than they were (apparently because of penny pinching and pandering to the greens)...

That said I wouldn't be too comfortable with one that's going to be empty (or below) 99% of the time, so here's my crazy idea: painted plastic dummy on top, long wires on bottom to actual batteries (or regular "external" battery if supported)?

maxtherabbit wrote on 2022-11-19, 12:39:

what I meant is the systems didn't always even have the battery soldered to the board in the first place […]
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flynth wrote on 2022-11-19, 09:00:

Yes, I've seen that mentioned in many places. Still if possible my preference is to have "something" installed. My first PC was a slot1 machine so I don't know what was a common practice at a time of 386s, back then I could only browse magazines and dream of the time I'll be able to afford one 😀 , but I imagine huge majority of users back then simply used their built in battery (while it was still good).

what I meant is the systems didn't always even have the battery soldered to the board in the first place

flynth wrote on 2022-11-19, 09:00:

If anyone knows the type/model number of a small rechargeable lithium cell sized like one of those 3 in a typical nickel battery please let me know. The remaining 2 could be just shells and the middle could be lithium if one of the right size exists.

you CANNOT use rechargeable lithiums in place of the NiCd battery - lithium requires charging circuitry which these old boards simply don't have, and doing it anyway can result in a burst or incendiary cell

Many small lithium cells these days have a 1s bms in the cap of the cell. Not all though. But you can buy them separately and shrink tube them on.

If the circuit is limited to the normal voltage and amperage range of the cell. A 1S (one series) setup is pretty straightforward. It’s when you get more than one series you start to have balance and over voltage concerns for individual cells.

A bms is never a bad idea though. It’s just that there is a lot less to go wrong in a single cell 1S configuration with known voltage and anperage ranges.

More than 1S always requires a BMS if charging is occurring no exceptions.

A balancer, is not the same as a BMS. A bms Is a full featured protection system. That may include a balancing circuit.

Those small lithium cells definitely need a BMS. Is there some sort of standard naming convention for batteries with BMSes? An extra letter in the name etc? If not I think I'll 3d print a dummy, I'll put it in shrink wrap so it looks the part. As real battery I'll use an external 18650 lithium cell with an external bms.

Here is an example of a 1s bms

You get them from somewhere like ali express or alibaba