It’s not uncommon for there to be more than one specification of battery for laptops - one that is standard size and another that contains more cells and offers longer running time (usually at the expense of being a bit bigger and sticking out the back a bit, or raising up the rear end).
If it’s the right brand and it says it’s for your machine, it’ll be fine. If it’s a compatible, it’ll be as fine as an off-brand product can be. If it’s the wrong battery for your machine, it almost certainly won’t fit into the battery space at all - as there seems to be no standard physical shape or size at all for laptop batteries.
Hell, I don’t know. I am holding the thing in my hands as I type and I can’t see any voltage numbers.
I don’t understand this idea of it will be bigger/longer and stick out the back. This is an 8-9 inch battery which “clicks” into place underneath. I’m not sure how it would be able to make the proper connections if it doesn’t fit.
what kind of laptop? these batteries usually use cylindrical lithium ion cells (typically the 18650 size) and a higher capacity version will add another “stack” of cells in parallel. e.g.:
The other thing I will caution you about is that a lot of the batteries out there are third party knockoffs from unknown Chinese manufacturers, and may not actually work out of the box. These batteries have circuitry inside that monitors cell state and controls charging, and the laptop’s firmware needs to be able to communicate with that. Some of these battery vendors want you to install a dodgy “BIOS update” to make it work, and IMHO the hell with that. If it’s still available from the laptop manufacturer, it’s far better to get a legitimate battery from them.
A higher capacity battery will be bigger in one of the directions not critical to it fitting onto the recess in the laptop body. Instead of fitting flush, it will click into place and there will be a ridge or bump on the outside profile of the machine