Take your battery to a place that sells batteries and have it checked. If it is gone to where old dead batteries go, then you will have to purchase a new one.
If cleaning the post and recharging the battery doesn't solve the problem, you may need a new one. Don't run to the nearest *convenience store* and buy a battery.
Sometimes the battery will build up a lot of corrosion on the outside of the cable clamp. When this happens, usually, the inside part of the clamp and post will create a hard metallic-like surface. This stops the flow of electricity from the alternator to the battery.
Remove the battery terminals from the battery post, if you have the *post* type, and clean the post and the inside of the cable clamp. If you have the side mount just loosen the 8mm bolt and clean the terminal where it comes into contact with the battery. Clean the part on the battery, too. :-)
The best way to use a *trickle* chargers is to charge the batter all night, or all day, whichever pleases you. You can try charging the battery. If it runs down again, then you need to do something.
Course, you'll have to run real fast after you hit the start position in order to see if the lights go out...or have someone out there watching for you.:-) You can purchase a small inexpensive battery charger at most malls, or parts store.
A simple way to tell if the battery is at fault is to turn the headlights on and turn the ignition switch to start. If the lights go out, then the battery is probably at fault.
If it goes, *click-click-click-click*, and so on, it may just be a low battery. A low battery that makes the starter *click* a few times doesn't have enough *juice* in it to turn the starter over to turn the flywheel over to turn the crankshaft over to make the engine start...phew!