The dual PRAM battery 1400c/166

[3lectr1cPPC]

Spinning this one out from the 540c restoration thread to avoid going full off-topic.
Basically, one of my 1400s, the /166 unit, had two separate internal PRAM batteries and I have no clue why. Anyone know? Everywhere else I’ve seen and my other units have one.

Best photo I have is a still from a time lapse I did for a yet to be released restoration video I’m working on. Clearly visible though, two bays.

 

[LaPorta]

Very interesting. I remember seeing the cutout in the metal on mine and wondered why the heck they would do that....and now I see that there may have been a variant. I am curious as to where the second one (the left one) connects to.

 

[LaPorta]

I can also verify that the take-apart guide only shows a single battery and only specifies how to remove one.

 

[3lectr1cPPC]

From what I remember, there was an extra flex cable segment branching off from I think the part for the normal always there PRAM battery, that went to the other side of the trackpad module for that second battery to connect to. It's a flex cable mess in there.

I unfortunately don't have any better shots, and I'm not exactly in the mood to tear down my 1400 again.

Also, this was a 1997 manufactured unit, so it is a later one.

 

[LaPorta]

You can see in the photo in my thread of another member's 1400, there indeed is a space on their 1400, but there was no battery present. The 1400 take apart manual photos show no such space on their 1400. We seem to have a genuine mystery here. I have a 1400 spares pile that I will have to look at someday and see how many have or don't have this.

 

[3lectr1cPPC]

Now that I'm thinking about it, the upper housing itself is installed in the parts machine, so I could go get photos of that. But I'm fairly certain that the dual-battery ribbon cable itself and all that is inside my working 166 unit, as that ribbon cable had the most clicky button. So I don't think I'll be getting many photos of that unfortunately, really don't want to tear it down again. Risks the plastic and such.

 

[3lectr1cPPC]

Apparently the eBay seller of the 1400 batteries has a dual-battery unit too, see the description: https://www.ebay.com/itm/325598692922
That makes two of them.

 

[LaPorta]

It is still strange to me that none of this appears to be documented in Apple's own service manual. The service manual I have does include the 166, so I would assume it would be in there.

 

[3lectr1cPPC]

Maybe it was only late revisions? Makes me wonder what purpose the 2nd one served. My guess would be a sleep mode battery, like many PCs. Many PC laptops would have one battery for CMOS and another for keeping the system alive in sleep mode while you swap out the main battery pack on the go. Those sleep batteries were always NiMH chemistry though, not sure if the PowerBook Lithium PRAM batteries allowed you to do that or not. The 3400 and 2400 might have since they did use those NiMH batteries. Really not sure as I don't have any PowerBooks with both batteries working, only one or the other.

 

[LaPorta]

Well for sure the single battery keeps memory contents: I swap batteries in my 1400 all the time with it asleep.

 

[cheesestraws]

Small data point for you: none of my 1400s (or the ones that have passed through my hands) have had two batteries.

 

[croissantking]

I noticed the space for another PRAM battery pack on the underside of my 1400c's palmrest too. I thought it was a little odd, like a left-hand drive vs. right-hand drive thing. Who would have thought some machines shipped with two packs? Not me. Quite intriguing.

 

[LaPorta]

Curious...did we ever figure this out?

 

[MacUp72]

maybe they planned and produced a different location for the PRAM battery mid-production and then abondoned that idea.
the most telling detail would be indeed where the cable of the second one went to.

 

[mari3311]

All PRAM built-in batteries in PowerBooks from PB1400 to PBG4Ti operate at 6.0V, except for PB2400, PB3400, and the first PBG3 (Kanga), and the only difference is the number of battery cells used (2, 4, 6 pcs).

The link is now broken, but

　　Tech Info Library 30580: 　"PowerBook G3 Series: Backup Battery Purpose and Life"

states that the sleep mode can be maintained for 4 minutes for battery replacement on the go.

I also think that 3lectr1cPPC's guess is correct as to why the PB1400C is the only one that uses two PRAM batteries (4 battery cells in total) unlike the other PB1400CS.

(I don't know if the 1400C consumed more power, but at least it provides more retention time for replacement, and since the PBG3 Series and later use at least 4 battery cells in total, it is more natural to think that this is the standard.)

 

[LaPorta]

The thing is, all of the 1400c models I’ve taken apart only have the one battery. Only one thus far has had a cutout in it’s shielding for another, but it was not present.

 

[3lectr1cPPC]

I also think that 3lectr1cPPC's guess is correct as to why the PB1400C is the only one that uses two PRAM batteries (4 battery cells in total) unlike the other PB1400CS.

All my 1400s have been 1400c units, not 1400cs units. Only my 1400c/166 had dual batteries.

 

[aladds]

I had a 1400cs/166 with dual batteries. Don’t have it any more to look at, though.

 

[croissantking]

Small data point for you: none of my 1400s (or the ones that have passed through my hands) have had two batteries.

So I just finished recapping your parts 117 machine, and I found that it has two batteries present. Remembering this discussion, I took some photos of the arrangement before defusing the machine.

The batteries are wired in parallel, so the voltage should be the same. I guess it just means the amp-hours are doubled?

 

[3lectr1cPPC]

Ah, so that explains it - just extra capacity. Maybe these can keep the system alive in suspend mode while the main battery is swapped out? A lot of PC laptops could do that, but they usually used a Varta NiMH pack rather than a lithium rechargeable.