Current solutions for low-cost and secure systems have ended up trading effective encryption schemes for lighter encryption schemes to ensure longevity in battery-powered applications. Here we demonstrate the potential to apply an effective and lighter encryption scheme, such as AES-256, in a low-cost battery-powered systems-on-chip (SoC) without demanding excessive energy. We accelerated AES-256 with a custom instruction along with an enhanced memory access scheme. Measurement results from a fabricated SoC featuring a RISC-V based 32-bit processor indicate a 900 fold improvement of AES-256 computing energy efficiency compared to pure-software implementations. The memory access improves the energy by 3 times an standard push-pull hardware implementation.