Why isn't a T420 slice battery able to be used with a T420s?

[jamiphar]

I've been trying to find an answer to the question, but I haven't been able to. Why is it that the slice battery that's offered for the T420 is incompatible with the T420s? The battery uses the docking port and both laptops share the same port. Is there some other difference, like the layout of anchoring clips or something? I can see that the battery has grooves to accommodate for a 9-cell battery on a T420 and that the battery would stick out from the back of the laptop, but I can't see anything that makes it uniquely compatible with the non-s models.

[jayton4]

I've been trying to find an answer to the question, but I haven't been able to. Why is it that the slice battery that's offered for the T420 is incompatible with the T420s? The battery uses the docking port and both laptops share the same port. Is there some other difference, like the layout of anchoring clips or something? I can see that the battery has grooves to accommodate for a 9-cell battery on a T420 and that the battery would stick out from the back of the laptop, but I can't see anything that makes it uniquely compatible with the non-s models.

From the best that I can see in the pictures, it looks like the T420s does not have the spot for the latch in the back right corner. Also, the dock connector is farther back on the T420s than the T420. Physically it looks like it would fit the T420s, but would stick out the back a lot more than the T420, and you would have to hold it on the entire time instead of latching it on. It would cause a lot of problems if it becomes attached and detached often while you are moving it.

Electrically, I do not know. Perhaps there is something in that connector that does or does not allow the battery to work?