Charging your 12 volt battery is extremely import, this will not only maximise performance it will also extend the life of your battery.
There are two main types of chargers automatic chargers which automatically detect the battery capacity which then apply just the correct amount of charging current for your specific battery, this type of charger will stop charging when the battery is fully charged, the other type is manual chargers which do not detect the battery size and will continue to charge the battery unless switched off.
Check Before Connecting
Before you charge any 12 volt battery you must make sure your charger is suitable for the size of battery you are charging. Each battery charger model is designed for a certain range of battery size (this will be confirmed in your charger user manual) using the wrong charger on the wrong battery will damage the battery permanently, or in very extreme circumstances can cause a battery to explode, so make sure you check before charging your battery
Connect to Your Battery
To connect your battery charger to your battery you must ensure that positive goes to positive and negative to negative to avoid shorting the battery. The order in which you connect should be positive first followed by negative. (When disconnecting do the reverse disconnect negative first followed by positive)
How long should I leave my charger connected
If you are using a smart charger then you can leave the charger permanently connected, the charger will stop charging when fully charged, the charger will then go into what we call maintenance charging mode which sends a small pulse charge periodically to maintain voltage. With manual chargers you do have to be very careful that you do not leave connected too long as with this type of charger you can overcharge (overheat) the battery which can cause permanent damage.
Calculate How Long a Battery Will Take to Charge
If you need to calculate how long a battery will take to charge there is a very simple calculation for this - example let's assume the battery is fully discharged (flat) the battery capacity for this example is a 10Ah battery, in this example we are using a 1 Amp output charger, you would simply divide the battery capacity in this case 10Ah by charger output 1 Amp (10 divided by 1 = 10 hours) of course these charge times will vary depending on how flat the battery is for instance of the battery was only 50% discharged then you would half the recharge time by 50% which in the example would now be 5 hours recharge time and so on...
The chart below shows you the voltage readings you will get for various states of charge, your battery should never go below 10.5 volts, going below this voltage will cause permanent damage to your battery which may not recharge again