According to todays safety regulations safe level of voltage for humans is 120 volts of direct current. I found a page that says Type VII, IX and XXIII boats had 145 volt battery system, so I'd say that is still in the safe range. No harm done if the current flows through your body.
"Normal charging" (characterized by 2.34 Volt tension)."
(Thats 62 cells times 2.34 volts = 145.08 volts)
http://www.uboatarchive.net/BDUOrder2.htm
Addition:
Found from uboat.net article
Technical description of cells
full charged voltage 2.1 V (Volts) = 130 volts
charging voltage without gas up to 2.4 V = 148.8 volts
http://www.uboat.net/articles/id/54