parallel or series charging

Ok been researching parallel and series charging. Which is actually better for charging lipo??

If I understand this right series. you just add voltage together and charge it 2-2s would = 4s.

The charge rate would stay the same.

Parallel you just add the capacities together so you could charge 2-5000 mah packs like it was one 10000mah or at 10 amps.

The wattage need for both ways is the same.

16.8v x 5amps = 84 watts 8.4v x10amps = 84 watts.

If I understand this correct you can take (batteries mah/micro charge amps) x 60 = approximate charge time in minutes Micro charge amps is say 5amps x 1000 = 5000 mca

Assuming a 50watt 5 amp charger and 1c charge rate

So a parallel 2-2s 5000 8.4v x 10amps = 84 watts needed only 50 watts available can only charge at 50watts/8.4v = 5.95amps so 5amps 10000mah / 5000mca x 60 = 120 min.

so a series 2-2s 5000 mah 16.8v x 5 amps = 84 watts needed only 50 available so can only charge at 2.98 amps 50watts / 16.8v = 2.98 5000mha / 2900mca x 60 = 103 min.

90 watt charger 20 amps and 1c charge rate hyperion 720i

parallel 2-2s 5000 mah 8.4v x 10amps = 84 watts needed 10000mah / 10000mca x 60 = 60 minutes

series 2-2s 5000 mah 16.8v x 5amps = 84watts needed 5000mah / 5000mca x 60 = 60minutes

1 2s by itself 5000 mah / 5000 mca x 60 = 60 minutes

so on a 50 watt charger you could save about 17 minutes in charge time.

also if you take the numbers run them in the traxxas charger which is 80 watts but only 6amps you 100 minutes for parallel an 63 minutes for series.

I guess I am asking if I understand this correctly?? What are the pros and cons of both ways??

Is it really beneficial to charge in series if your charger is under powered??

How does the balance work when doing parallel?? I understand how it does it in series.