LOL... title says it all, yet you ask about speed... had to laugh.
Battery power - unimpacted by the size of the SSD. Remember, these drives are D-Latch memory chips, not spinning platters. There are probably great benchmarks around showing how they use less power than platter drives etc etc... but I wouldn't expect you to find any evidence that a 512 GB SSD uses more or less power than a 128 GB.
As for performance... that is a completely different question, and quite honestly, handled by many threads in this forum with extensive analysis.