UPDATE!

The LSDJ cart started acting the SAME way with my other gameboys, so I replaced the battery and now it works on all of them!
The only thing I can note with the DMG is that when you start playing whatever notes you have tracked out, the contrast on it goes up a tiny bit.
Is this normal?
I still have the option to send it back to the person who sold it to me.
Should I do that?

Very normal. And I quote...:

Full article here.

The LSDJ cart started acting the SAME way with my other gameboys, so I replaced the battery and now it works on all of them!
The only thing I can note with the DMG is that when you start playing whatever notes you have tracked out, the contrast on it goes up a tiny bit.
Is this normal?
I still have the option to send it back to the person who sold it to me.
Should I do that?

Timbob wrote:

Bear in mind that lsdj is quite a heavy program to run, and backlights do add extra strain on your batteries, so some contrast/light reaction is normal.

It also depends sometimes on how the backlight was attached. There are various points to choose, and some respond more to power fluctuation then others.

Anyway, in short: yes, maybe, could be, could be not.

Also, I hear a lot of people talking about replacing the battery inside the EMS when the gameboy starts to act weird.

Now it could be just me, but isn't that battery not just for saving the ram? How does an empty save battery effect the rest of the gameboy?

Agh! You're probably right! But would taking the save battery out ruin/delete my LSDJ saves?

Yes, if you replace the battery, it will wipe the ram. So back up first before you do that. After that you can just re-upload the sav and all is peachy.

I do see a difference between my two EMS carts tho. With the older one the screen light/contrast seems to react more to lsdj then a new version, but it could also be a board revision.

With my drag 'n derp I get very little interference.

Timbob wrote:

Addition!
Rechargeable batteries are usually not as strong as normal batteries. They also provide 1,2 volts usually instead of 1,5. So there's that as well.

Right. Are they NiCd batteries? These also have the lowest mAh output.

Nah, they're Energizer. But they do have 1.2 volts like Timbob said. This might be the problem.

Addition!
Rechargeable batteries are usually not as strong as normal batteries. They also provide 1,2 volts usually instead of 1,5. So there's that as well.

I did not know this.

What the DMG really needs is a fifth battery slot. xD

This is genius.

Bear in mind that lsdj is quite a heavy program to run, and backlights do add extra strain on your batteries, so some contrast/light reaction is normal.

It also depends sometimes on how the backlight was attached. There are various points to choose, and some respond more to power fluctuation then others.

Anyway, in short: yes, maybe, could be, could be not.

Also, I hear a lot of people talking about replacing the battery inside the EMS when the gameboy starts to act weird.

Now it could be just me, but isn't that battery not just for saving the ram? How does an empty save battery effect the rest of the gameboy?

Agh! You're probably right! But would taking the save battery out ruin/delete my LSDJ saves?

Rechargable batteries have always given me problems.

Addition!
Rechargeable batteries are usually not as strong as normal batteries. They also provide 1,2 volts usually instead of 1,5. So there's that as well.

Right. Are they NiCd batteries? These also have the lowest mAh output.

It also depends sometimes on how the backlight was attached. There are various points to choose, and some respond more to power fluctuation then others.

Anyway, in short: yes, maybe, could be, could be not.

Also, I hear a lot of people talking about replacing the battery inside the EMS when the gameboy starts to act weird.

Now it could be just me, but isn't that battery not just for saving the ram? How does an empty save battery effect the rest of the gameboy?