It should be quite obvious that as it stands, single use batters are more or less useless.
Sure they might find an occasional niche or need, but by in large useless.
Which is why I propose two things:
1) Allow SU batteries to be crafted with charcoal dust. Charcoal dust would have the only sole purpose of being used in SU batteries.
Using one charcoal dust, 1 redstone and 1 wire would make 5-6 SU batteries. This would give the SU battery some role in the early game, as an alternative to directly using charcoal in coal generators.
2) Add a more powerful SU battery that would use glowstone, gunpowder, fuel and redstone. 
Where is glowstone dust, is Gold Wire and is redstone dust.
Using coal fuel can will yield 6 SU batteries that hold 20,000 EU, while using biofuel can will yield 3 of said batteries.
This would make an alternative to solar panels and reactors in the mid game.