Small Engines (Lawn Mowers, etc.): Troybilt, battery terminals, riding mower

Question
I dont have the model number but I just have a simple "how does it work" question.

I have a Troybilt 18 HP 42 Inch riding mower that is approximately 5 years old.  Last year after sitting for the winter (I live in the deep south!) as normal I had to charge the battery before it would crank.  Charged it... cranked right up.  But the next time i went to use it (about a week later) had to charge it again.  EVERYTIME I had to use it I had to charge it so I bought a new battery.  STILL Have to do a short charge before it will crank every single time even with the new battery!  I dont know ANYTHING about small engines (or big ones or anything) but it seems that there is probably something similar to an alternator on a car that would keep the battery charged.  How does a small engine work (what part keeps the battery charged?)

I would like to have at least an inkling of how it works before i pay money i dont have to try and get it fixed.  Any help would be appreciated.

Answer
Claudia
You may have one or more problems.Something may be draining your battery while it is off. Usually it may be lights a key left in mower or a blade solenoid. The first thing you should try is unhook the battery terminals first the ground see if there is a small spark,if there is something is draining the battery. How a battery gets charged is from a small item called a battery charge rectifier.This rectifier is located under the flywheel housing.