Appropriate battery replacement for my A3000

Question

I know the interwebs are full of information relating to the replacement of batteries for various computers, and the Amiga's are no different. But before I do anything rash, I wanted to ask for some input.

My A3000 still has the original clock battery on the mainboard, and obviously this needs to be removed and replaced.

I thought I was going to replace this with a CR-2032 watch battery socket so I would be able to replace the battery when necessary. This easy ebay solution looked promising... However I noticed the original component is clearly labeled 3.6v and 60mAh (milli-ampere-hours).

A CR2032 is rated at 3v but should last ~200mAh. Is the CR2032 a good replacement choice, or will the lower voltage cause any unexpected weirdness? And what kind of battery-life can I expect? I've got some 486SX/25 mobo's from forever-ago and I swear the CR2032's are still working...

Finally, and perhaps most importantly I was a little freaked out when I read this:

A special note for A3000 users: The RTC has a small amount of memory also backed up by the battery which is used to store settings for the motherboard SCSI controller. After replacing the clock battery, you will need to use SetBatt-1.2 from Aminet.

Usage: SetBatt A

This clears the "amnesia" bit. The SCSI controller settings may also have been lost due to the power interruption to the RTC and may need to be altered depending on your SCSI devices.

• taken from this guide

My concern stems from the fact that my A3000 has the original beta Kickstart 1.4 ROM which it uses to boot the actual Kickstart image from the SCSI hard drive (Kickstart.rom). The absolute last thing I want to do is disconnect the on-board battery for a few days and loose something vital to my ability to boot off the SCSI drive.

Can anyone offer any further details?

As always, all input is greatly appreciated!

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Addendum

After reading the excellent responses below, I took the time to re-assemble my Amiga and downloaded SCSIPref from Aminet so I could double check my current settings. As expected, all values were defaults.

I also took the time to put together a few 'rescue' disks with things like SCSIPref, JRComm, and other essentials (SuperKickstart 1.3/3.1) just in case I have to do anything weird after replacing the battery.

Finally, I took some voltage readings off the battery while the charging circuit was both powered and unpowered to (attempt) to properly size a Schottky diode for reverse current protection. I'm going to solder the CR2032 holder right to the motherboard.

Thanks again for the help!

Answer 1

Don't wait, just clip it. Come back when you're done. You look dangerously close to getting the goop on the motherboard which is effectively malignant cancer for electronics.

Now that you've clipped the battery, you need to decide on what replacement you want to use. Unfortunately, the Amigas originally came with NiCd batteries which despite being prone to a bunch of issues they also have different charging requirements than (say) LiOn. Because of this, you can't just solder in any old battery since bad things could happen.

That being said, you can use any battery you want (to provide between 3 - 3.6V) as long as you disable the charging circuit. Typically you would do this by connecting a diode inline to the battery which allows the battery to discharge into the motherboard but prevents the motherboard from charging into the battery.

I found a page here that seems to do a good job explaining things: http://members.iinet.net.au/~davem2/overclock/batt.html

Answer 2

On all my retro computers, I tend to replace the on-board batteries with cables and a double AA battery holder like this that I can store off-PCB (typically, I fix it somewhere within the computer using double-sided tape) to make sure leaking batteries can never again damage the PCB. Normal AAs by far won't last as long as the original or Li-Ion batteries, but I don't care. In case the original used a rechargeable battery, I put some NiCad batteries in the holder. (You could, however, do the same with longer-lasting lithium batteries in case you find a suitable holder).

Some of my computers tend to stay on the shelves for a rather long time, and I really don't fancy having to check the batteries regularly.

With regards to NVRAM content: It really doesn't hurt to have a backup of it or at least noted somewhere in the computer what configuration needs to go in there and a matching procedure.

Answer 3

Even if the battery powered memory loses its contents, you don't really risk losing the ability to boot.

The settings that are stored in the memory for the on-board SCSI controller are all performance-related, if the battery data is lost they would all revert to their defaults, that are (appropriately) the more conservative choice.

The only non-performance setting is the SCSI id for the controller, which would reset to 7, that has always been the Amiga convention (and there were no reason to change that if memory serves).

I actually don't remember ever reading back in the days that the loss of the battery contents prevented ever anyone from booting from the HD...

Answer 4

Get yourself three AA or AAA NiMH ready-to-use rechargeable batteries, a triple clip and fit the clip where nothing can ever get damaged. The NiMH get you the exact same voltage as the original battery but an insanely long buffering period (>a year with 3x AAAs).

I put the clip outside on the back, so I can take them out and speed charge them - Miggy doesn't run as much any more as she used to...

Losing the SCSI settings doesn't hurt by the way unless you changed the host ID or your HDD requires a very long spin-up wait (replace that one with a decent HDD while you're at it).