You should remove the sticker and check what's below, but I don't think that matter.

BIOS chips from that era usually are EPROMs that doesn't need any external battery. You'll need to find the NVRAM chip to find what voltage does it need (but remember that there may be some components like diods between the solder pads of the battery and the chip).

Most 386 motherboards had an external battery header that enabled you to connect an external battery pack to the motherboard.

Based on past experience, in some cases, 3x 1.5V = 4.5 V wasn't always sufficient to keep all the CMOS settings (for e.g., it would lose the date and time). For that reason, I normally connect a battery pack that holds 4 AA size batteries for a total output of +/- 6V.

Just be aware that, if you connect your external battery to the same connection to where your onboard battery was, then you need to place a diode on the + line to prevent the battery pack from being recharged.

I would therefore suggest you rather use the external battery header.

I have removed the rechargable battery as it was in an early stage of leaking and yes I want to use an external battery from the external battery header on the motherboard but since the rechargable one was 3.6 volts I thought the external one had to be around the same, is there a way to test at first if 3 AAA batteries is good enough or a way to get the datasheet to tell for sure?

Post a picture of the whole board. You don't need the datasheet of the bios chip, you need it for the real-time clock chip, which may be a standalone chip (e.g. Motorola MC146818A or compatible) or may be integrated in one of the bigger chips (e.g. 82C206 peripheral controller). In the case of 146818A, it operates anywhere between 3 and 6 volts.

The BIOS on your motherboard is most likely of the 27C512 EPROM type - you can easily confirm this by using a utility called Navrátil Software System Information (http://www.navsoft.cz/products.htm) to save your BIOS to a file on your hard drive. If the file size is 64 KB (512 k/bits ÷ eight) then you know you have a 27C512 EPROM chip. However, also refer to what Zup & quicknick has stated.

You can refer to this website for some guidance, particularly the subsection titled "DIY external battery holder using 3 x AAA alkaline batteries": http://pc-restorer.com/replacing-cmos-batteries-in-old-pcs/
You can either use AAA batteries or AA batteries, doesn't really matter (whatever battery holder is available).
3x 1.5 V batteries giving a total of 4.5 V should work - if you see that it still isn't keeping all the settings, then try 4x 1.5 V = 6V but, test the voltage output with a multi-meter before increasing the voltage.
Incidentally, just this weekend I realised that my 386SX wasn't keeping its settings and discovered that the batteries inside my battery holder wasn't making proper contact (helps to have a multi-meter around). Prior to that, I've never had issues with the battery holder supplying the motherboard with a total of +/- 6V.

The above is also based on discussions in older threads about what other users had experienced. Sometimes a total of 4.5 V is just not enough to keep all the settings (which is ironic, since once would expect that 4.5 V should be enough if the original rechargeable battery only supplied 3.6 V).

The "input" from the ext_bat header passes through 1, 2 or even 3 diodes in series, each one giving a ~0.5v voltage drop. This should be easy to deduce on each board, by visually checking the traces and using a multimeter.

Out standing guys I dont know where you learnt all this but I thank you from the bottom of my heart, Quicknick I found a Motorola chip with "MC M6264CP20" and it has some more letters and numbers under that the picture is here:

http://s836.photobucket.com/user/sierragames/ … 9h5vul.jpg.html

and the rest of the board is here:

http://s836.photobucket.com/user/sierragames/ … %20Time%20Clock

GabrielKnight123 wrote:

Out standing guys I dont know where you learnt all this but I thank you from the bottom of my heart, Quicknick I found a Motorol […]
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Out standing guys I dont know where you learnt all this but I thank you from the bottom of my heart, Quicknick I found a Motorola chip with "MC M6264CP20" and it has some more letters and numbers under that the picture is here:

http://s836.photobucket.com/user/sierragames/ … 9h5vul.jpg.html

and the rest of the board is here:

http://s836.photobucket.com/user/sierragames/ … %20Time%20Clock

The M6264CP20 chip is more likely to be a 8K * 8bit tag ram.
The RTC / CMOS RAM should be inside the H82C206 chip above the M6264CP20 chip.
The diagram in the datasheet includes a 6V battery, which is higher than the commonly used 3.6V batteries of that time. I'd say try with 3x 1.5V batteries and see if it works.

Thanks Lazibayer thats excellent I will try some fresh batteries when the shops are open in the morning, I dont know if this will work but I contacted AMI and asked them for a datasheet for the motherboard but its so old now I bet they dont keep info like that for this long.

I found this board that looks very similar to yours.

That looks like mine yes and I have the AM 386DX-33 with a 64Kb cache, the motherboard has a spot for an NPU (I dont know what a NPU is) but is this just a Co processor like a maths co processor? would one help to play Dos games?

GabrielKnight123 wrote:

That looks like mine yes and I have the AM 386DX-33 with a 64Kb cache, the motherboard has a spot for an NPU (I dont know what a NPU is) but is this just a Co processor like a maths co processor? would one help to play Dos games?

Yes NPU stands for numeric processing unit, aka FPU or math-co. Some games will benefit from the aid of the math-co.