Dear people: I noticed that when I twist the throttle rapidly the 4-leds digital voltmeter indicates the voltage lows, even with full batteries. Before disassembly the batteries case I like to ask you about this.
I weld all the main connections from the battery to the controller and replaced that original weak fuse holder with a round one and a 15A tubular fuse.
I built a resistive load of 1.2 ohms with some Ralco resistances and I
connect it at the output of the batteries case. The voltage is 38.4 V
without load and 35.5 V with it. The intensity is 11.5 A.
Could be the internal resistance of batteries or any parasitic resistance of the key switch or fuse holder?