I get that Battery's strength lies in enabling the Technology cards, but its vanilla abilities are strictly worse than Herbalist. Compare to Black Market--it's only a terminal silver and worse than other $3 Terminal Silvers in it's vanilla ability, but it's (usually) better than the $2 Terminal Silvers: Duchess (which helps your opponent) or Embargo (which is a one-shot). Meanwhile, Tournament is a Peddler (except when it isn't), making it reasonably priced at $4.
Maybe have Battery be +2 Cards, +1 Buy? That way, you still might buy it for the buy or draw even if you don't need the Tech cards. Otherwise, since Battery is so key to the Tech Cards, you might want to move its price point to $2, for the same reasons that Chapel is $2--you don't want to force people to have to open Battery/nothing on a $5/$2 opening (if you intend for Tech cards to be truly powerful.) Alternately, you might want to make Batteries non-terminal (e.g. $2, +1 Action, +1 Buy) so that people aren't penalized by buying several of them. Or you could make Batteries an alternative Treasure, like Potion.
Also, how does the 'while this is in play' clause work? I get that playing Battery allows you to buy Tech cards (or Workshop them, Remodel into them, etc), but it will probably do weird things with City, the game-ending conditions, etc. Is that a feature or a bug?
Finally, Mad Scientist is worded weirdly. The way it's written, if I trash a Battery or spend a Fuel token, and my opponent reveals Moat, I can now discard a Battery for more Fuel. But that's only relevant if I have two Batteries in my hand. Is that what you meant?
Otherwise, you can have Mad Scientist set aside a Battery or Fuel token, have everyone gain a curse, and then trash/spend the set-aside item if anyone did get cursed.