My main concern would be fire load.

It's ok to say they hardly ever explode but simple fact is the potential is still there for them to do so.

Using Hydra as an example where we had a short on the Nicad battery packs. It was realtively easy to deal with with very little heat or flame except very locally to the packs. It was easy to pick up and run out of the building with and it was realatively easy to keep cool whilst we got the packs out (one went first and then with a cascade effect took out the others and tried to set them on fire too). That said they didn't stop trying to catch fire again until out of the robot and completely taken apart from their mounting brackets.

In the event that someone has a large lipo in their robot it has potential to explode. It happens before you know about it and then you are dealing with a fire rather than smoke. If there is more than one pack in there and one explodes what do you do? Do you go in and fight the fire in the full knowledge that there is a further pack in there which may explode or do you leave it and contain it and risk it spreading and burning down the arena and sports hall? (and worse disrupting the show!!)

IMO there are safer packs to use and absolutely no reason for anyone to take a risk on LiPo's in heavies.

Andy