What would happen if two batteries connected in parallel or series?

1. Two batteries in series:
voltages are summed (doubled)
current remains the same for both batteries as for a single battery

2. Two batteries in parallel:
currents are summed (doubled)
the total voltage remains the same for both batteries as for a single battery

For examle:
one X battery = A volts, B amps of current
two X batteries in series = 2*A volts, B amps of current
two X batteries in parallel = A volts, 2*Bamps of current

But please make sure:
When connect batteries in series, please make sure two batteries internal resistance and capacity are same;
When connect batteries in parallel, please make sure two batteries internal resistance, capacity and voltage are same.