Add the capacities of your packs to calculate the charge rate

Single 5000mah sized pack
1c = 5 amps
2c = 10 amps
4c = 20 amps

2 x 5000mah sized packs in parallel
1c = 10 amps
2c = 20 amps

5000mah and 4000mah in parallel
1c = 9 amps
2c = 18 amps


Cheers