You probably mean Hippo VL+:
https://theretroweb.com/motherboards/s/octek-hippo-vl-2

You can use this adapter to replace the NiCD one:
https://www.amibay.com/threads/nicd-to-cr2032 … adapter.120160/

Otherwise the external battery holders usually have 3x AA or even 4x AA batteries. So 4.5 to 6V. I use the one with 3x AAA.

I understand that the battery soldered on the motherboard has to be 3.6v rechargeable, I could replace it with a similar one. About the external batteries also have to be rechargeable? Puede ser también de 3,6V?

Yes you can replace the battery with exact same type. If you use an external battery connected to the P8 - 4 pin header they cannot be rechargeable as there is typically no charge current on those pins (the near by diodes prevent it and reversing the battery).
Use standard AA alkaline type for external batteries. Usually pin 1 is + and pin 4 is - but you should double check it...

Thanks very much Horun!!!
One question, What is the minimum voltage for the external connection? Can I connect a 3.7v type T1AA battery?

Very thanks for help Horun!!

Get this famous doc (source pc-restorer.com).

On my side, I get always a DIY external CMOS batteries LR6 battery pack (3x1.5v - that's fine and work well).
The advantage is that the motherboard will no longer be exposed to batteries.

When hooking up an external battery to a Vippo VL+ 486 mainboard, it's essential to use the correct voltage. Make sure to check what your mainboard needs. It can be a battery or a cell, as long as the voltage matches the required.

I had to figure out something similar with my gadgets. I found a helpful article about different types of D batteries at https://batteriesglobe.com/d-vs-d2-vs-d4-vs-d … -d12-batteries/. It was instrumental in picking the correct battery type and voltage for my stuff. The right battery is essential for ensuring your device works correctly and stays safe. And one of these D batteries (like d, d2, d4, d8, d12) could work for your mainboard if they fit the specs you need.

I recommend a solution with 3 AA or AAAs. I don't know why people use CR2032 in these old motherboards. They go flat incredibly quick because they only yield ~2.7V after the diode drop. Older RTC chips need 3-6V typically.

The old PC-style Motorola RTC pulls about 150uA in standby. That will kill a CR2032 quickly. CR2032s are meant for modern RTC chips that pull a handful of uA or even nA.

I‘m using a 3 x 1.5V pack in 3 different 486 machines and they‘re working great.
They came without a connector so I just cut up some CD-ROM music cables and used those connectors.
One of those PCs had a new barrel battery soldered in by the previous owner. But although it saved all the settings, the year was always wrong - something like 2091 😊
Of course I got rid of it!

Kouwes wrote on 2024-01-16, 22:08:

I‘m using a 3 x 1.5V pack in 3 different 486 machines and they‘re working great. They came without a connector so I just cut up […]
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I‘m using a 3 x 1.5V pack in 3 different 486 machines and they‘re working great.
They came without a connector so I just cut up some CD-ROM music cables and used those connectors.
One of those PCs had a new barrel battery soldered in by the previous owner. But although it saved all the settings, the year was always wrong - something like 2091 😊
Of course I got rid of it!

CD audio cables work well. You can also search eBay for "1x4 Dupont Cable".