The board is this one:
http://fcelectronics.mybisi.com/product/rs232-ttl-converteradapter-kit-max232-for-avrpicarmgps
The first of four battery connected with board fails (negative voltage). Other three batteries retains its spec voltage of 1.2V.
The four Ni-MH gives stable 4.8-5V.
The batteries are not protected by any diode from reverse voltage.
The same VDD (sorry, mistyped), aprox. 5V source, share the project board and the Max232 board.
I hope it make sense now.