What is wrong with my LG chocolate phone and/or my charger? :(?

When my phone was starting to lose its battery in the middle of a call I was on tonight, I put it on charge only for it to turn itself off. Whenever I try and charge my phone now it will not turn on or work, but when I take it off charge it turns itself on, says the battery is charging and the battery bar keeps going up and down as though it is charging, it lasts for while then turns itself off again. It will not do anything at all when I have it on charge, it will not even turn on, but if I leave it on charge for a while then take it off it will turn on etc as described before and let me text and make calls as usual whilst saying it is charging(obv impossible when the charger isn't even attached), then will eventually go off again (as though the battery has died)! Can anybody please explain why my phone is behaving so erratically and/or what the solution is? Any help is much appreciated! No liquid has been in contact with my phone as far as I am aware!