IMO, the first purchase should be a Wattmeter. It is considered standard safe proceedure to store lipos at 3.8 volts in a cool, dry place. You will only Know what the remaining voltage is in your battery by testing it, either with a voltmeter or our std tool, a wattmeter. Turnigy (Hobbyking has a 130A unit for like $25)
And yes, get yourself a better, balancing charger asap! This will go farther to prevent problems than anything else you can do. Check out the I Charger's at Progressive RC.com. Not esp cheap, but will allow big expansion as you get into electric flight, like parallel charging of multiple batteries ( up to 6). FWIW flytwice
