How do I get 12V 260mAh from 4x 6V 130mAh solar cell panels?
Sure, theoretically you can get 12V 260mA from 4 solar cells with 6V 130mA (not mAh!).

Just like that:







simulate this circuit &ndash; Schematic created using CircuitLab

However:


Solar cells rating is maximum rating, at full direct sun.
You need some voltage and current regulation for safe battery charging - 8x NiMH is 8x1.2V = 9.6V nominal, and 11,2V fully charged (8x1.4V). 12V charging is too much for uncontrolled charging.