Yes, most likely the battery inside. It is easy enough to replace. You can buy it from any drugstore. Unscrews from the back. Make sure you are unsnapping it from the band as well when you aren't using it. This conserves battery power. Best way to do this is un-snap single snap, leaving second snap snapped to the monitor, as long as one snap is undone, it will stop sending a signal and draining the battery.
It depends on the package you get. the heartrate monitor is extra and it does come with a strap. included in the package is a charger with USB connector, ANT+ connector to upload your workout to "GarminConnect" to analyze, plan, and monitor your progress. overall, this a good watch.
I have had mine for awhile and the band hasn't broken or given me any problems yet. Its plastic thoe so it will probably where out eventually. The charge for the battery works great and hasn't given me any problems either. Its magnetic so it sticks straight to the watch.