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WTB: External CMOS battery (4.5v I think)

D

dracos

Experienced Member
Joined
May 4, 2011
Messages
202
Location
Northern VA - USA
Just putting together a 386 system to do play my old DOS games, got a great mobo/cpu/npu combo, but getting flack from the onboard battery. I was hoping to get the system setup first, no luck with that, now I remember all the pain with those old systems, still brings back good memories.

I know:
a) I should remove the onboard battery anyway as it will eventually leak.
b) I could probably build my own, but I really would like to push the "EASY" button on this and buy one!

So if you have one lying around, or know who has one (in stock!) let me know.

$20 shipped to 20147 via paypal sound fair?
 
Whose 386 system is it? Is the battery rechargeable or not?

I routinely substitute a battery holder and 4 AA alkaline cells for the special batteries. The AAs last their shelf life (at least 3 years)--and I can pack the whole thing in a small plastic bag to contain leaks.

Your local Radio Shack carries a wide range of battery holders, pretty much all for under $2. If you're replacing a rechargeable battery, add a blocking diode in series with the battery pack.
 
I usually Velcro a 3x AAA holder to the inside of the case, and use the wire/header from a PC speaker to connect to the motherboard's external battery header. If the pack you're replacing is a 3.6V rechargeable, just use NiCd cells instead of single-use AAAs.
 
It really doesn't matter--the MC146818 (and its clones) used as the RTC/CMOS on these old machines is rated well in excess of 6V for normal operation. Given that there's at least a diode's worth of drop (~ 0.7V) in the battery circuit (more, usually, since there's usually a series-pass transistor too), it's entirely safe--many old AT case kits shipped with a 4-cell holder.

You could use a 3 cell holder, but that would leave you with a bit less headroom as the batteries discharged. If you were replacing a rechargeable battery, the added blocking diode would bring the voltage somewhat lower than you'd want.
 
It's a Opti 495sx chipset mobo, I believe a DTK, but I have had problems identifying the exact make and model. (no printing on the mobo identifies)
I do have the usual 4 pin connector for external battery. This is not the usual one you find when you google, it has 6x 16 bit slots, with an 8 bit on either side of the 16s. Loaded with an AMD 386DX40, the matching NPU and 256k of cache. Not being able to find the exact mobo model it is hard to determine whether the onboard batt is rechargable or not. Or even exactly where it is, though I am sure if I pull it out and look at it closely I can find it and snip it safely.
 
I've got a (mumble) 386DX40; don't recall the chipset, but the onboard battery was one of those blue Tadiran solder-ons (rechargeable). I snipped it off without even removing the motherboard from the tower case and plugged in a 4-cell AA pack to the 4-pin connector. It works fine.
 
If it has an onboard battery, remove it NOW! If it leaks, it will destroy traces on the motherboard.

If it's one of those 3.6v lithium batteries soldered to the board, I usually just replace it with a coin cell holder and use a normal CR2032 if there is room on the board. If not, you can use a AA holder and velcro it someplace in the case. Wrap it in plastic/tape or some other holder, and mount it away from the board, that way, if the batteries leak, it won't damage anything.

-Ian
 
He's already got a 4-pin external battery connector on the board; he might as well use a 4-AA holder. No sense in trying to solder a new battery on the board--you'll just have to repeat the exercise again in a decade.
 
RetroHacker_ said:
If it's one of those 3.6v lithium batteries soldered to the board, I usually just replace it with a coin cell holder and use a normal CR2032 if there is room on the board.
Click to expand...

Err - replace a rechargeable battery with a nonrechargeable battery, soldering the holder into the same position as the original?

The board will attempt to charge the battery if it is attached to the solder points for the rechargeable battery.
 
kishy said:
Err - replace a rechargeable battery with a nonrechargeable battery, soldering the holder into the same position as the original?

The board will attempt to charge the battery if it is attached to the solder points for the rechargeable battery.
Click to expand...

The original lithium batteries aren't rechargable either...

-Ian
 
Thanks for all the thoughts! Seems my local radio shack is staffed by kids who don't know a resistor from a capacitor, unless it's something in a Play Station 3 game. Short version, they were out :( , good news is I found everything (and more) that I needed here. I should now be able to do any custom jumpering stuff I want to. $150 bucks later. See why I wanted the easy button?

http://www.pololu.com/

But I've been meaning to get this stuff for a while, now I won't have to worry about finding stuff when I can make my own.
 
I have what you are looking for. It's a "TADIRAN TL-5242/W 3.6V LITHUIM BATTERY". It has a wire that connects directly to the pins on the motherboard. If you would like to buy one or more, let me know. Thanks.
 
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