Your hold luggage is limited by weight not content. Obviously.
But you cannot take a laptop computer or a laptop battery in hold luggage.
You are limited to (this changes all the time) about 8g of Lithium in Li-Ion batteries. More than that and they won't allow it.
Unless it's a dangerous piece of kit, there's not much else to say on the matter.
I don't know how you're supposed to work out what 8g of lithium means in respect to a battery - but it's safe to say that laptops, rechargeable camera batteries etc are carried on, not put in the hold.
I've travelled with hard drives, camera gear, cables etc and nobody has ever even questioned/searched the contents.

