Gakken CGL and Futuretronics Battery Covers not identical.

[Lumps]

As a newbie to this forum and forums in general I may be posting something that is well known , boring or inappropriate for discussion.
Recently I was have a little realtime comp with friends on the Galaxy Invader 1000.
I was putting batteries in a few of them to get going and got them a little mixed up. And it turned out the CGL and FUTURETRONICS covers would not fit the GAKKEN unit.
I had always seen them as identical apart from country of manufacture and badging etc.
I was wrong.
Kinda easy to see why on examination. The GAKKEN does not have battery springs like the others do and therefore requires less space in the compartment.
While this is more of a statement than anything, I ask the question, Is this common with other games released by different companies.
Mainly as I do pick up different units that do not work to rat parts for others assuming that they are identical in size.
Also as a newbie, I am happy to hear if this is not Forum type material.
Also, Thanks for the add Rik.
To wrap it up, my names David and I live in Australia. Thanks.

[Rik]

Kind of surprising that they'd go through the trouble to make different molds for manufacturing like this..

I've noticed that the Coleco mini-arcade games aren't all the same. Battery covers for Frogger or Ms Pac-Man (can't remember which) don't fit correctly on the other games. There's something slightly different about them.