I think I lost my x201 due to a Chinese battery. After I used the replacement battery I think a Mosfet transistor burned out inside. The laptop wouldn't turn on, and if turned on it closed in matter of seconds.

Although the actual cause might be different (I'm no expert) I've become cautious of super cheap Chinese 9-cell batteries.

Oh absolutely. It's a shame there's not a reputable company making replacement compatible batteries for old laptops and phones. I guess the original companies have design patents to try to stop this.