as everyone else has posted, more details are needed. I am assuming you got a sealed lead acid battery, if that is the case you NEED to keep it as close to fully charged at all times as possible as sulphication may start.
to check if battery is working get an automotive probe ( it looks like a screwdriver with a light inside and a wire out of the top usually with an alligator clip on the end) and use that to test if it has ANY charge left. to check if battery is holding max power it needs to be fully charged.
I must also point out here something, you may have bought an SLA battery thinking it'll last as long as the one in your car does, but remember the battery in the car is constantly recharged via the alternator, if your charging plant is too small for what you are using it for then you will constantly drain the battery. this is NOT good for SLA's
give us as much detail about the battery and what you had it hooked up to as well as the charging plant you used as you can so we can help you out more.