Of course we must be aware of all of the obvious things like not charging when in the car. Making sure there is plenty of ventilation as charging a battery will generate hydrogen gas which is explosive. Think the Hindenberg. Always connect the positive side first and make your final connection away from the battery , incase you generate a spark. Other than that use a good quality Volt/ohm meter to check before and after readings. Battery is not charged fully until 12.6 Volts or higher. Charging a battery is like cooking a thick steak. Cook it Low and slow.
Other wise it is like cooking too fast and hot, which is burnt on the outside and raw on the inside. Low amperage for several hours. If this is needed because the battery drew down while not in use, you need to fully charge the battery before you do any diagnostics. Clean and tight.