I believe you should have all of your 36 cell panels connected the same, in parallel.
It is my fault if my previous comments have you confused. I intended to say in some places, sometimes, 40 cells could be better than 36 cells. I did not intend to say 72 cells are ever better than 36 cells.
The 36 cell arrangement is great. The very minor gain of 2- 36 cell series panels would be a much much greater gain if placed in parallel.
About meeting the charging voltage... If the cells can not meet the charging voltage, the amps they can produce is very small.
Rough example (very rough)...
With 2- 50w PVs capable of 2.5a (average) for 5 hours per day. They give 25ah/day. In series they only give 12.5ah/day.
A very bad day comes along. One PV can not make charging voltage. 2 can. But, they can only make .2a for 3 hours on such a day. Or only about 0.6ah. The battery would have been better with 25ah yesterday from parallel PVs, almost 42 times better.
Using 4 PVs (2 sets of 2 in series) with a total of 13 PVs, the output on good days will be 18% better. On very bad days, the total output will be very small and insignificant.
It is better to have 118% on Monday, nothing on Tuesday, and 118% on Wednesday.
Put them all in parallel. There will be power to use everyday.
G-