Latitude E6500 battery

I use my laptop while commuting from home to the office (very questionable, i know, and the battery initially used to survive the entire trip and recently started to die out before the 1h it takes to arrive.
Indeed, I started recently compiling more than before which takes more cpu and therefore more battery. I run a lightweight linux variant.
I have the standard battery. Is there some improved battery I can purchase to replace my existing one? Do batteries start dying out quicker with time?
The laptop is probably 4 years old or so.

Regards,

 

Batteries lose capacity with usage and a 4 year old battery could have easily lost half of the original capacity (many are close to dead at that age). I would expect that there's a Linux utility that can report the battery info which include (i) design capacity - more or less what it was like when shipped; (ii) fully charged capacity - what it can hold now when fully charged; and (iii) current capacity (actual charge in battery at the time of checking).

Once you have found and used a utility that can give you this info you can then decide whether to replace with either a new standard (6 cell) battery or the extended (9 cell) battery.

John