Batteries:
4 x GreenSaver Silicone Power 12 V 38 AH
Charger:
GreenSaver 5-stage Green Battery charger model HB 48050 (48 V 5 A)
Conversion time and cost:
New EUR 1495, got this for EUR 950.
Top speed:
52 km/h on the meter, not GPS checked yet, only with freshly loaded batteries.