13" Macbook Pro running Lion loses battery fast?
Battery life depends greatly on use. 238 charge cycles in 5 months by most standards is pretty high. More importantly if your following the guidelines Apple has published for their battery use are you getting usage times that are in line with their estimates? Coconut battery isn't always accurate, its best to trust the built-in tools for diagnostic information.

You can also check System Information (Lion) or System Profiler (10.6) under power to get an idea of the stats on the battery. Double check to see what your Full Charge Capacity and the Charge Cycles are. 

Any Apple Store or Authorized Service Provider can run diagnostics on the battery as stated by Wheat Williams. If it is faulty it's covered by your one year limited warranty.

Also check for run away processes you can check Activity Monitor, these could be draining the battery faster and driving up charge cycles.
http://support.apple.com/kb/TS1473