My Weird Warlock Fix...

[diplomancer]

I didn't know that, but that sounds good to me. Doubling them is not enough for a standard adventuring day.

Alternatively, have warlock slots recharge in one minute (so you can use them each combat). They are probably intended as "encounter powers" so just codify them as such (this assumes that you ban coffeelock, of course).

The best solution, or at least the one that most approximates their expected output on a table with no short rests, is probably to give them a 2/LR ability of recharging their slots with a 1-minute ritual.

If tracking 2/LR is considered too complicated for any reason, double their slots and let them recover half once per long rest.

This second method can also be used for tables where the average SR/LR is 1. Keep the ability as is, but double their slots and let them recover half on a short rest. It's slightly less predictable (sometimes there will be 2 SRs, sometimes 0) but some people might consider that a good thing.

Oh, and either bring their 3rd slot down to 9th level, or at least give them a Rod of the Pact Keeper. 11th level was a mistake.