Laptop Memory Upgrade

[Remilia]

So planning to upgrade my laptop memory at some point maybe this week. Not sure which or how to go about it.

Laptop is a Lenovo X230 with the selection of
i5-3210M clocked at 2.5GHz, despite Win 8 manager showing 2.9GHz underload for whatever reason.
Exchanged HDD to a 256GB Samsung 840 SSD.
Two RAM stick slots.
Normal Win 8 64bit
With their upgrade from TN to IPS panel though this shouldn't matter at all anyways.

RAM stick is some unknown one that I can't figure out at 1600MHz 4GB.

Plan is to essentially end up with min 8GB.
The 4GB is basically keeping me from doing certain things when I have just one game open which is why I want to upgrade.

One of the thing for me is battery life though. I don't play heavy games like FFXIV without it being plugged in. Low settings, yadi-yada.
I don't know how much the RAM voltage will affect it if any so it would be a nice thing to keep in mind, also wondering if I should just go with 1 8GB stick or 2 4GB sticks.
As far as I know only 1600MHz and 1866MHz are compatible with this. Obviously 204 pins.

Basically, want laptop memory upgrade. Which one. Lol.
Still mainly for school work but would be nice to not be bottle necked by RAM which is a very odd feeling.

[Cyrops]

First of all:
16GB max
7 / PC3-12800 1600MHz DDR3, non-parity,
dual-channel capable, two 204-pin SO-DIMM sockets

Those are the memory specs for that laptop. If you want 8gb total, I would recommend buying a 4gb stick so you have dual channel.
You can order from Lenovo site.

[chazus]

Lenovo charges an arm and a leg for a 4gb module ($63)

Just get this: http://www.newegg.com/Product/Produc...82E16820208576