Nothing drains NTUs faster than damaged turrets. You can almost literally watch the NTUs drain out of a base if all the turrets are destroyed or damaged. During a fight if just one person keeps the turrets going you'll dramatically decrease the drain on the bases resources.
Another frequent problem I've noticed is that teams will take a base, fill it up with NTUs but forget to repair the turrets before they leave. 10 minutes later the base is again at 40-50% power and still dropping. The base becomes a perfect target for a small squad to hit and drain. You wind up with a neutral base behind your lines being hacked.
For any squad trying to puposely drain a base, destroying the turrets is the best option. If you take out the generator then a small icon pops up next to the base showing that it is down. This gives away your position to anyone looking at the map. Just destroy the turrets and most people will just assume it is low on NTUs and the most you'll have to deal with usually is a lone ANT runner. A lot of TR on Markov have been using this tactic and I'm always suspicious when I see a base dropping power.
So, repair the turrets people.