So in the end of the season my bike started acting up...from say September till winterization.

One day the bike would not start, so I hooked it up to either car (not running) or a battery booster (plug in the wall)...and she started up right away....took the bike out at higher than normal rev range for 20min or more....the next day would not start again..

2007 gs500F...20,000K

Is it my battery? Or charging system?

The bike runs normal in operation after boosting it..

If it the charging system, how do I test it....if its the battery (which I presume is the problem) where can I find a $50 battery?

Thanks

some new battery chargers can test the battery, although i dont know if that helps you or not. you could also take a multimeter and just test the battery voltage after letting it sit for a day or so after having the bike running...if it's not ~12V then you may have a bad battery.

if you do have a newer battery charger, you can check to see if the charger has a desulfurization mode. i don't know how it works except that it cleans out the inside of the battery. the vector smart charger that we have does it, im not sure what other models do.

check basic stuff like the electrolyte levels in the battery as well. if any are low you can add battery acid (sulfuric acid iirc) or distilled water.

Batteries die almost every year if not run daily.
They die if you dont have them on the charger every 1-2 days in winter if not riding.
They die if you dont have enough water in them.
They die if the acid is too dilute and it freezes.
They die if the acid is too strong by eating the plates.

They die if you look at em funny ... and I know for sure you look funny ... so yea ...

Walmart batteries have the drain on the wrong side but all else is the same so its fine.

$50 - get a sealed ES12BS from walmart and put it in sideways. Re do the cables a little, piece of cake.

Pay more for a sealed battery that fits right side up - ES10 some or other - GSJack has a post on that.

Cool.
Buddha.

Check the voltage when the bike is running. If it's around 13-14 volts your charging system works. I'm not 100% sure what voltage the GS is using for charging, but at least more than 12,5 volts.

auto parts stores have a handheld tester that can diagnose your battery and charging system.  it is free to use.  I would suggest hitting that up 

I put a Scorpion AGM battery in last Mar 09 and it's been excellent, best bike battery I've had so far.  I got a short ride in the day after Christmas and then the weather went down for a couple weeks of very cold snowy days of below freezing highs for a couple weeks.  When I started up again last week it fired right up after cranking it three times for 5-10 seconds.  In the past with conventional batteries I would have ground it down and had to jump start it after sitting that long in winter.  The AGM seems to maintain much better starting voltage while cranking after sitting in the cold. This is my 26th winter of year around riding here in NE Ohio.

I paid $50 for the Scorpion which has gone up to $54 now and includes shipping to anywhere in the lower 48 states.  You'd have to check with them on shipping to Canada.  A real bargain I think for a proper size AGM that slips right in and has no vent to worry about and no constant summer acid level checking.  I was always forgetting to check mine and running it half dry and my last couple of Walmart batteries didn't last too long.

http://www.batterystuff.com/power-sports-battery/sYT10L-A2.html

Perfect, I'm gonna get a Scorpion....wasn't looking forward to getting another conventional battery...this will work well....it is also $54 via Ground to Canada, this should be good....so when I get it...I just have to hook it up to a battery tender until season starts again?

BUT do you guys recommend I buy it couple weeks before season start (so buy it later?)....so that I dont have a brand new battery sitting around (possibly deteriorating)...