Will getting a new battery improve performance or is just for electrical purposes?

 

No battery will give you more HP.
BUt----------
I think it was 03SETE who put in an Odyssey 680 for a 23 lb weight savings over stock.
Some say ea. 12 lb in weight reduction is equal to about 1 HP.

 

4th Gen GoldenGlory
i gave him an extra yellowtop i had laying around
he said after swapping it, the car seemed much stronger, and the S/C also kicked in a lot stronger.
my belief....yeah...a weak battery will affect power.

 

Other than starting, and at idle with the lights on, power is'nt coming from the battery-- it is coming from the alternator. The excess power from the alternator then goes back to the battery if it needs it to keep it charged. The battery other than at idle just acts like a big capacitor to stabilize the voltage.
Unless you have a hybred honda or Toyota, a battery should not be able to give you more HP.

 

Yeah, the battery acts as a stabilizer for voltage. Theoretically, a stronger battery (putting out more voltage) should result in less AC ripple in the electrical system's DC output, and more stability (less AC ripple = electrical system voltage won't drop as low between wave crests from the alternator's output)... so it is conceivable that a fresh battery can improve overall performance over an old worn-out one, but I doubt the difference is that big.

More info on AC ripple in an alternator's output: http://www.eatel.net/~amptech/elecdisc/charging.htm