Hello there,

I happened to "Re-Start" my RC career about a year ago (after a 30 year break) with the Slo-V and I went through several tweaks/upgrades that I can share with you. This are the steps I went through:

* First of all I did what you were asking about - adding more battery for two purposes:
1-Increased power
2-Increased flying time
* The wing area/characteristics of the wing can handle the extra weight without any problem only after a very simple reinforcement of the wing.
Epoxy a couple of carbon tubes (not rods) to the underside of the wing somewhere behind the leading edge.
I also later added Extreme tape to further stiffen the wing.
* After being the biggest consumer of propeller shafts at the local stores and emptying out their stock, I modified the power plant again with a brushless
outrunner motor (Park450) and could now eliminate the gearbox completely as it was swinging the 12x4.7 with grace.
This upgrade was great, now I had a plane that didn't make any noice, if flies silent... and power for vertical climbs when needed (to get out of impossible
situations that otherwise would have resulted in a crash...
* Last power modification was the replacement of standard cell packs to Li-Po.
Lower, no-much lower weight, Now I could easily stay up 15-20 minutes with a 1500mAh and unlimited climb.
* I also had to stiffen up the v-tail to avoid flutter.

I loved this setup and this is where I finally earned my wings...

Good luck

Stryker_Viking