Firstly I would suggest that you check whether the problem is really with the charger or the Dc9099 Battery itself. All rechargeable batteries deteriorate over time, especially if they are left fully discharged for a long time or are frequently left on charge for extended periods.
If you have a spare battery try charging that.
You can test the charger itself with a digital multimeter (electrical test meter). 1) plug in your battery charger to mains supply and switch on. 2) Set the scale on the test meter to 200 volts DC Voltage (V--) 3) Insert the test meter probe wires in the sockets on the meter marked "Com" (black) and "V/Ohm (red) 4) Touch the other ends of the probes onto the metal contacts on the charger. It doesn't matter which way round you do it
If the voltage reads in the region 20-25V (will be either + or - depending on which way round you place the probes on the contacts )the charger is probably working okay.
If you have a battery charger that is for US Voltage (110)volts you can buy a 240V-110V step down converter quite cheaply here. http://cpc.farnell.com/_/mw2p-045/45w-230-110v-ac-ac-adaptor/dp/PW00942?crosssellid=PW00942&crosssell=true&in_merch=true&