Batteries, for me, are just to keep going until I plug in again. If you really rely on battery usage, you should probably trade off performance (use less memory.)
Laptops typically have teeny (even though many gigabyte) single platter, single head drives that do not have great throughput. If you want your laptop to perform anything like a desktop machine, you really do not want it spapping to disk any more than necessary. Virtual memory with a slow disk is not your friend.
Just my opinion. Take with as much salt as necessary.
Hugh