I've worked my way through 3 android phones and, after trying most of the popular custom roms for each of them, I've always ended up with a cyanogenmod rom (or one built from their source) because they seem to be the most stable and offer built-in battery/performance efficient functions. (It's been great to get Kitkat on to some of the older phones, via cyanogen, it's breathed new life into them, before liberating to friends.)

Also use Xposed Framework for further customisation and battery/performance tweaks.
A Faux123 kernel for more of the same.
A wakelock dectector and Greenify to deal with wakelock apps, to squeeze even more life out of a single charge.
So with all that on a Moto G I'm getting 3 to 4 days life out of single charge with a fair amount of usage and wifi/data on throughout the day (managed by Auto Data app).

What phone have you got?

great phone

i have installed cyanogenmod on my old phone, it was good and faster than the stock rom, i also prefer stock android to sense ect. now i have a new phone (huawei ascend p1 lte (9202l), i have got clockworkmod on it but have had no luck with a rom. i could probably compile from source but i dont have linux installed and dont know how to set up cygwin.

cyanogen has verified support for the nexus 5 so it should be easy to install.