Many chargers will not show voltage at the leads unless a battery is connected. The battery must also be at a certain voltage level as well. If it is too low, the charger will not recognize that it is there.
We used to have an audi S4 cabrio that the wife would rarely drive. the battery was stone dead. When I connected the charger, it wouldn't recognize the battery, and I had to bring out my Marine battery, and hook up jumper cables to the dead battery while on the charger to "trick" it into recognizing, and charging the dead battery. She drove it the auto parts place, and they swapped it out for her.
You could test your charger in a similar fashion prior to installing your new battery.
2010 sunset trail ST26RK, 2012 Nissan Titan SV crew cab, equalizer hitch / Pine Grove, Pa