you need the right type and size of cable. This is mostly just looking at the 2 ends. most common are 1.6mm, 1.8 or 2mm square on both ends. sometimes it's a split end on the driven side. You should be able to look at the drive, and look in to see the right size/type, or Identify what drive brand it is, like CEV or whatever. I think Bats are VDO
Next is the threads to thread onto the drive and onto the speedo, m10x1 is the most common, for both ends.
From a quick search it looks like yours should be a VDO with 1.8mm square on both ends with m10x1 thread.
Then length is just however long you need to reach from the drive to the speedo, 60cm is pretty common, measure it. too long just leaves extra cable, too short wont work (obviously). 60cm looks like it works for Batavus.
Theres also a chance the speedo itself is messed up, You'd need to get one made for the right speedo drive or it'll read incorrectly. again should be VDO.
or far more commonly issues are with the speedo drive. it's the little thing on the axle and probably has a tab into the front wheel. sometimes you can repair em just bending the tab back in. There's 2 main types, one or 2 tabs. It'll match cutouts on the wheel, but both can work - single tab can still drive if theres 2 cutouts, and double tab can work on a single if you bend one of the tabs in. Also gotta match the axle diameter, bat is 11mm. And theyre directional, so it's gotta be correct side (right vs left drive) Finally theres a gear reduction in the drive also thats gotta match to read correctly. stock VDO on a bat should be Left hand, double tab, 11mm axle, 1.6 ratio drive with the 10x1 threads. It should be marked 17/17 or something. Looks like this is maybe correct: https://www.treatland.tv/NOS-vdo-speedo-drive-METAL-version-1-p/nos-vdo-drive-metal-version-1.htm but check the markings on your drive before replacing it.
That all said, it sounds complicated but it's usually not. Worst case you got a mismatch, you can take off the face plate and make your own back plat image, like paint on corrected speeds. Alternately you can go with a bicycle speedo, they just need a magnet on the spokes and one on the forks, and then you set the functional diameter and get a digital speed readout. Or you can get a GPS speedo, theyre pretty reliable now. Or or, just mount a phone and use a speedo app, this is easiest and most accurate.
Final option? fuckit. you can only got 30ish anyway so you're either going 30, you're stopped, or you're trying to get from one to the other as fast as it can.I dont use a speedo on anything.
So what I'd do, tryn pull out the cable and measure length and end sizes and check that it's whole and not frayed. If the cables OK, plug it back into the drive and remove the end on the speedo, spin the wheel and check that the cable speedo-end spins. If so, the drive is probably OK. If not, take off the driver, check the tabs and make sure theyre complete and engaged with the wheel properly. you can check the speedo by disconnecting at the driver end and chuck it in a drill and see if the needle moves. you gotta have it pressed all the way in. If you have a bad cable, easy - replace it with the right one. Bad drive, tryn fix the tabs, grease it, see if you can get it back working. if not check the markings and replace it (or bail and go digital) and if the speedo is bad, same advice.