2008 M15x Outsurvives my Sager

Well, my Sager 8150 from early 2011 died last week. Faulty GPU/Motherboard. It's likely the motherboard and paying $550 on top of a diagnosis isn't really something I'm willing to consider for an old laptop. What that leaves me with is my even older M15x from 2008 w/

1600x900 Resolution
i7-720QM (Big bottleneck)
GTX 460M (Reasonable).

At the very least I need to ask where to purchase a reasonably priced (~$60-120) 6 cell or 9 cell battery. This battery no longer holds a solid charge (laptop dies after power adapter is removed). I've mostly been playing Guild Wars 2 which is pretty processor dependent. I'm unsure as to whether an upgrade to a 920XM or 940XM would make much of a difference.

I'm curious whether I should just save up and build a desktop to outlast everything or upgrade my old M15x to one of the unlocked processors which would no doubt require both a fresh battery and I'm led to believe a stronger more consistent PSU from an M17x or M18x?

It's more than enough for me to play League of Legends comfortably albeit the fact that it loads slowly. Essentially what I'm asking is what/how are the most cost-effective upgrades I can make and are they worth doing?

 

Regarding the battery:

If you upgrade to a 920xm or 940xm, it WOULD make much a difference. However, these extreme processors have a huge power draw when overclocked which will kill your new battery quickly or you'll get throttled to unbelievable low clocks.
Therefore, if you want to play on battery, I don't think upgrading the m15x is recommended.

 

I have no intention of playing on battery. I'm just tired of the machine powering down because the battery doesn't hold a charge at all. When the adapter is unplugged it immediately shuts off. What's the standard power-adapter for running the XM processors?

 

If you OC (considering it's an XM, you will) you will need a 210W or 240W PSU with the middle pin pulled, OR with a right angle adapter(with the middle pin pulled). I'll explain below:
The high power draw of the CPU and GPU exceed the limit of the original power adapter. The m15x will try to limit the power draw to about 150W-180W in order to protect the adapter. This limit is being checked through the adapter signal wire(the middle pin). Breaking the connection of this wire breaks the limiting, which means your laptop will not throttle anymore, you will be able to OC the hell out of it, but you will not be able to charge the battery.

Therefore, you need a 210W or 240W PSU, AND a right angle adapter and remove the pin on that adapter instead of the PSU. You will play games using this adapter, and remove it when you want to charge the battery(or use your old charger).

The right angle adapter is this: Right Angle Connector Converter for Dell HP Compaq Laptop Power Adapter LC90B | eBay