Switching between AES and a highly performant algorithm I want to de/encrypt several binary files rather frequently on a normally battery-powered device. My goal is to use AES-256 when the device is AC-powered and a highly performant algorithm when it's battery-powered to save power. I appreciate that the level of security will be compromised. 

Is there a performant algorithm that provides "decent" security? I see that Blowfish fares a bit better according to this analysis, but the difference is rather small over AES-128. Given that the paper is almost 10 years old, are there good alternatives out there today?

Is AES-128 supposed to be the standard for something decently secured and highly performant?
Yes, AES-128 is intended to be the standard block cipher for building a secure and efficient symmetric cryptosystem using some block cipher operating mode, like CTR for encryption or GCM for authenticated encryption; efficiency can be particularly good when there is hardware support for AES and GCM.

There might be better choices in the case at hand, like for a 32-bit CPU ChaCha (perhaps combined with Poly1305 for authenticated encryption), or one of a plethora of  lightweight block ciphers. If the device is 8-bit, and speed/efficiency paramount, one might even consider the deprecated and partially broken RC4, although its security is questionable even when discarding the beginning of the keystream.

Notice that keeping secret the key of either of these algorithm is hard in a non-security CPU assumed in the hands of an adversary, to the point of being best considered impossible facing a competent and determined adversary. And in a modern security CPU, you might have AES in hardware (thought often, optimized for security rather than speed).