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[jaymac]

  running graupner Wiesel with 3 graupner 600 7.2 v  supplied by 6V lead gel and 2 x speed controllers /  I believe these are OK up to 8.4v so would there be much gain in switching to some 8.4 packs Nimh ( preferred )  of which I already have some. If so what Pros/Cons benifits    not too technical please
thanks
Jay

[unbuiltnautilus]

Possibly fit either slightly smaller diameter props or shallower pitch ones.  What are your speed controllers as the current drain will rise quite a bit with the increase of only 2.4 volts?

[jaymac]

Hi Mtronics  Viper 20A and 40A  but changing anything other than the batteries for me is a No Go area.I'm not looking for more speed more towards slightly better slow to fast range control.

[malcolmfrary]

Thats an almost 50% increase in voltage and therefore current - the resulting power applied to the motor will almost double.  Whether or not an increase in speed is wanted, its going to be there.  There might well be an improvement in low speed response because the ESC will be giving more powerful kicks to the motor which should start it turning earlier and maybe more reliably, but I suspect that it will not be huge.
Fortunately, Graupner have (had?) the reputation of solid products with generous safety margins built into their specifications, so as long as the loading is not excessive, the motors should handle it OK.
For the same amount of energy stored, NiMH are considerably lighter than SLA. 

[jaymac]

OK tried with 2x 8.4's in parallell   does seem  abit smoother though water  too choppy to be sure .  sits and aan doesn't roll so much  with  weight being lower  so looks like the Nims win
Thanks to all for their input