50 in parallel need 50 x 0.02A = 1A of current. 2 strings, 2A That's going to take one big battery.
That will likely vaporize conductive paint too.
Can you run from 12V battery, strings of 4 or 5 LEDS? Will drop your current to 1/4 or 1/5 of an Amp.
Then one Logic Level, Low Rds, N-channel MOSFET to switch all the strings in parallel on & off.