For the 1000th time: not the cartridge battery. Pocket's AAAs are just too weak and the cartridge needs more juicy juice.
Try wall adapter and you'll see.

There's no reason why the gameboy pocket would drain the cartridge's battery. Besides that, the battery is just for the ram, and having a dead battery or even no battery won't cause symptoms anything like this.

Oh and pockets don't like EMS carts, they drain the battery in them.

I had the same problem, if new batteries don't work, try cleaning the battery contacts.

The pocket drains the ems carts battery.Probably the problem that you're having is that.You will need to switch the battery in it.There is nothing that comes to my mind that can cause it to behave like this.I am almkst 100% sure it's that.

If you write it on the pocket, you'll become aware of what it can't handles as you write it. It's not an issue of where it's written, but what the chip on each one can handle.

Gah, It won't even load LSDJ now. It just comes up with the Nintendo symbol then switches off.

Well this is annoying. So in theory it should be fine if I write the piece on the pocket as opposed to using the DMG?

I stopped using pockets cause they always crashed on anything I wrote. Colors can handle more than a DMG, Pockets can't, at least in my experience.

i can't imagine anything you've done being too cpu-heavy though (not a bad thing, btw )
although if you have vibrato playing on both pulses and the wave channel at the same time then that might do it

but yeah, you should be able to use LSDJ on the pocket without any troubles.

I wrote it on a classic gameboy. I thought that the pocket would be slightly more powerful? Whoops. That certainly would explain the weird behavior.

If you wrote it on a non-pocket, there's a huge possibility that the track is just too much for the pocket's CPU to handle.

It's not backlit. It's a USB 64MB Smart Card.

Is it backlit? Also, what kind of flash cart is it?

Yup, I did try new batteries.