Battery-less 128K ram card for HP 48GX

[mr-scorpio]

Hi there,
I recently purchased a 128K memory card at a reasonable price.
After installing it, I've managed to merge it with the 48GX internal ram, so I now have a lovely 256KB.

The intriguing thing about the card is that it DOESN'T use any kind of replacement battery. There is certainly no way to open the card, & no removable opening to insert a battery. It only has a write protect switch.
The card is made by: Microcards ?

Does anyone have an idea how this card functions power-wise?
Does it draw a tiny amount of juice from the calculator batteries to run it? - Even when the 48GX is OFF?
Does it contain a rechargeable 'battery' of some kind?
OR does it have some sort of persistent memory, that once written to remains resident until it is written to again, even if the card is removed? - OR if i were to remove the card, would anything stored on it would be lost?

It seems to be a professionally made card with a metal chassis.

Look forward to your insights.

Edited: 15 Sept 2011, 7:04 p.m.

[Dave Britten]

I think most of them have some kind of rechargeable battery inside the casing that trickle charges using power from the 48 while it's turned on. The 48 only supplies power to cards while it's turned on, so if you can power it off without losing data, the card battery at least isn't totally shot.

[Howard Owen]

The battery "door"is often hard to see on those things. If you press along the top edge of the card, you should find a inset drawer that contains the backup battery.

[Martin Pinckney]

Well, if there truly is no battery, then probably the card can only be used to augment system RAM while it is plugged in.