Because batteries are power sources not resistors, and therefore don't follow ohm's law. Also they don't have "a" current, they have a "maximum" current.
Does connecting batteries in series increase ampere capacity?
Connecting batteries in series increases the amount of voltage. It doesn't increase the ampere capacity. But two batteries connected in series means their positive and negative terminals will work together. For example, if you connect two 12V 30Ah batteries in series, you get a combined voltage of 24V.
Does putting a battery in series increase open-circuit voltage?
If you model a battery as an ideal voltage source in series with a resistance, then putting batteries in series will increase the open-circuit voltage by n times the number of batteries in series, but the short-circuit current will not change because the internal resistance also increases by n times.
When the batteries are arranged in series, the voltage adds up. Higher the voltage, higher will be the current drawn by your circuit. When the batteries are connected in parallel, the voltage will remain the same. (The current supplying ability will increase, but let us keep it aside).
Batteries last longer in parallel, because the voltage remains the same, but the amps increase. If you connect two 12v 50ah batteries in parallel, it will still be a 12 volt system, but the amps will double to 100ah, so the batteries will last longer.
Why is it important to connect a battery with equal voltage?
Equal Voltage: It is important to connect batteries of equal voltage to avoid imbalances and excessive currents in the parallel connection. Imbalance Risks: Connecting batteries of different voltages can result in higher-voltage batteries overpowering lower-voltage batteries, leading to potential performance issues.
Connecting batteries in parallel increases the overall capacity by adding the current output and energy supplied by each battery. This results in an increase in the total current in the circuit. It is a way to increase the amp-hour capacity without changing the voltage.