In order to know the time needed to fill the battery you need to know the capacity of the battery, without taking into account various factors charging time x current strength of charging amperes = battery capacity, for a 50Ah battery it takes about 30 hours. But the actual charging also need to consider other factors.

What are the factors that affect the battery charging speed?
(1) charging efficiency, power charger speed commonly used to express the power, it is easy to calculate, power = current × voltage, which is the ideal speed of the charger, but in the battery charging the loss of heat inside the battery, the battery internal resistance, etc. are affecting the current inflow, based on the different materials used in the manufacture of batteries, each battery’s internal resistance is different, we generally believe that this is in the loss of 20%, of course, this is only with the rough calculation. Of course, this is only a rough calculation.
(2) charging voltage, if you want to meet the full charge for a battery, you need an adapted power supply can do this, the 12-volt battery fully charged charger voltage cannot be lower than 12 volts, we usually use 12 rated charging voltage for 12-volt battery charging, but in fact the charger’s voltage is higher than 12 volts about 1.2 times, this is the premise of the battery is full.
(3) Battery capacity, as the name suggests battery capacity is to indicate the capacity of the battery stored electricity, pouring a cup of water and pouring a bucket full of water is not the same battery capacity is the biggest factor affecting the charging time.
(4) the battery’s C multiplier, have you ever thought that since the battery’s ability to store electricity is limited then increase the charging current is feasible, in fact, it is feasible, but he is not unlimited growth, in order to safety and unit time battery’s ability to take into account the battery each battery has developed a charging and discharging multiplier known as the C multiplier, in the battery to provide the appropriate current, you can appropriately increase the charging current, the current can not be more than the C multiplier.
(5) voltage (current) stability, the battery charging process charging voltage and current, not unchanged before the beginning and end of the battery will be the voltage changes, the real charging for the battery is a stable voltage stage, if the charging stage can be maintained for the battery can be efficient and safe charging, but if it is not stable will greatly reduce the charging efficiency at the same time there is also a danger.
(6) Battery aging, long time battery use battery will be subjected to different degrees of aging, aging battery in any respect will be subjected to different degrees of damage.
How to speed up the battery charging time?
(1) temperature, the battery is too high or too low temperature will affect the charging efficiency of the battery, the battery should be charged in a cooler environment.
(2) lead-acid batteries, clean terminal corrosion, replenish the electrolyte, lead-acid battery electrolyte loss and battery terminal corrosion caused by prolonged use will also affect the charging speed.
(3) Use the appropriate charger, for lead-acid batteries and lithium batteries have different chargers designed for them, if the lithium battery charger used in lead-acid batteries is not only ineffective but also damage to the battery.
(4) Retain the remaining power, the use of the battery discharge fully battery than the remaining power of the battery charging speed is much slower, retain 20% of the power is a good way.
Conclusion
When charging a 12-volt battery with a 2-amp charger there are various factors that affect the charging time, the battery capacity plays a major role in the time, and the use of a higher current charger can effectively reduce the charging time.