The problem is most probably the unstable output from the generators. This stresses the input circuits of switching power supplies/chargers, especially the bridge rectifier and "bulk" capacitors. When you test the charger with higher, but stable, voltage they behave well because of the smoother operation...
The above will affect also a linear circuit, with less problems.
If you study the datasheet of your battery (or an equivalent one), then you may find that the article you linked is not very relevant with the subject.
Taking information from manufacturer(s) you can decide of what charging mode you need/want.
Tip: the simpler to implement is a float charger. Next is the cycle use charger and the more complicated is the "topping-up" with load connected.
Bring the information and the specifications here to discuss it more specifically.