It was around 4 hours when new - reviewed here: https://books.google.co.uk/books?id=L2RD68Gg2 … epage&q&f=false
It doesn't compare so favourably compared to the other laptops in that test, but many of those were far heavier and may have had passive matrix screens, which draw less power.

I have no idea where you'd find a battery pack to replace it, see this example: https://www.energyplusbatteries.com/pf/6255/0 … t-Battery-Pack/
I have its later relative, the Portege 610CT which came to me with no battery. That was kind of a nuisance so I made a 3d printed space filler and that works, but it's no battery. Having a replacement battery now would require either re-celling an original, or reverse engineering the original and making something to work with that (which would be really difficult). The T3400 was one of the first Lithium Ion laptops, so it might not be the safest / most functional implementation to start with.

Have a look here for all the part numbers for batteries and other parts: http://minuszerodegrees.net/manuals/Toshiba/O … part%20list.pdf
Assuming that the T3400 and T3600 series share the same battery fitting, that would be PA2481U and PA2483U. My Portege 610CT's got the same chassis shape as the T3400/T3600 series, but I can't tell whether the batteries would be compatible.

Since it seems you do have a functioning battery to start with - try cycling it a few times to see if that helps, but it's quite likely a few cells in the parallel / series configuration have gone bad, severely limiting the capacity.

thank you for the response! As it was the battery was only lasting maybe... 10-15 minutes (after having in plugged in to charge for 6 hours), so definitely not the intended 4 hours. i will look into those links, i had trouble finding more detail about the battery itself so thats something at least, and will try cycling it as well. much appreciated, ill pop back in if i have any success.

Open the battery, figure out what size and type of cells it uses, buy new cells, replace, profit

If it's working for 10-15 minutes, that's usually going to be one of the cell sets in the series has failed, so the battery pack's highest voltage is 8.4 volts instead of 12.6 volts, then it'll drop below workable voltage very quickly. The energyplus battery page says it's 10.8 volts and 3300mah, so that'll be 3x sets of cells in series, each with 3x cells in parallel, or 3s3p. Checking my portege 610CT which is about the same, the dimensions all fit that theory.

Since it's one of the earliest Lithium Ion packs, just replacing the cells won't be especially easy. I mean, on the one hand you don't have to fight a battery management system's controller chip / eeprom, you could probably get away with just swapping out some or all of the cells. The downside is that getting new cells is not easy.
But it's still a lithium ion pack and there's safety things to be aware of when working on them, the cells need to be balanced with closely matching voltage before use, ideally have matching charging / discharge curves & wear. And it really needs a spot welder to fit new cells safely and a short or damage to the cells could cause a fire.

That said, I've done something similar with my Thinkpad 240 batteries recently - got some good cells from a new old stock pack, took out the old cells, spot welded new cells in, reset the eeprom and put it back together with care. And that resulted in 2x working packs where battery packs are no longer available.

You'd need a little spot welder - I use the BIFRC DH20, it's not great but works well enough for building a laptop battery pack. Alternatively, you could buy tagged cells, those could then be soldered into place if you use leaded solder & are fast.

The cells that I think are in your T3400CT's battery pack should be 17670 cells as those are what most early Lithium Ion packs used - you can find similar in Toshiba's other Lithium Ion laptops from the era like the PA2487U which you'll find in Toshiba's Satellite 4xx and 4xxx series and some others. Enough of those laptops have failed over the years that there are a few of those still good or partially good battery packs out there to use for donor cells.
For new cells, I've been trying out the 16650 cells as a replacement and capacity boost, need to finish that up on my Libretto 100CT sometime.

This is something I've been thinking about for a while, lots of these museum pieces - laptops and other portables lose a lot of their meaningful functionality when the batteries fail, but there's a lot involved with replacing them and I don't know of services or easy to follow / concise guidance to help with that. Something like the caps wiki seems like a good fit.