Everything wears out eventually. Plugs can become loose, as can cable connections, transformers can break down. But a half decent or better charger will be ok for decades. Which explains why so many of the mobile phone microUSB connectors fail after a year or two.
You do not say what type of battery you are charging, though it doesn't really matter too much. To check that a charger is providing a suitable voltage, it's easy to place a small meter across the supply plug. Set the meter to DC and put one lead in the plug centre or crocodile clip and the other to the outside of the plug or the other crocodile clip. If you use a digital multi-ranger unit, like http://www.ebay.co.uk/itm/New-Digital-Multimeter-XL830L-AC-DC-OHM-Meter-Voltage-Tester-Circuit-Checker-UK-/112050017035?hash=item1a16b3930b:g:wvQAAOSwnHZYV6dn it doesn't matter if you put the leads the wrong way round, as the meter will just give a negative voltage reading. The fact there's a voltage at all indicates that the unit is probably working okay. Under a no-load condition it will probably read higher than you need and drop to the correct voltage when charging. Hope this helps.