Examples disclosed herein relate to dual in-line memory module (DIMM) battery backup. Some examples disclosed herein describe systems that include a backup power source pluggable into a DIMM slot. The backup power source may include a plurality of battery cells electrically connected to a DIMM to provide backup power to the DIMM. Each of the plurality of battery cells supporting the DIMM may be electrically connected to a DC-to-DC converter in series and to each other in parallel.