Internal series battery and electrical device

An internal series battery, comprising:

• a series module, comprising battery units and intermediate current collectors;
• a number of the battery units being greater than or equal to 3, each of the battery units comprising a positive active material layer, a solid electrolyte layer, and a negative active material layer that are stacked;
• each of the intermediate current collectors being corresponding to and disposed between two adjacent battery units, and the two adjacent battery units being connected in series through the intermediate current collector;
• a positive current collector, located at one end of the series module and electrically connected to the positive active material layer of the battery unit at one end of two ends of the series module opposite to each other;
• and
• a negative current collector, located at the other end of the series module and electrically connected to the negative active material layer of the battery unit at the other end of the two ends of the series module,
• wherein the battery units comprise at least two first battery units and at least one second battery unit;
• the at least two first battery units comprise two battery units respectively at the two ends of the series module, the at least one second battery unit is inside the series module between the two first battery units;
• wherein an energy density of each first battery unit is greater than an energy density of each second battery unit;
• each first battery unit independently comprises a lithium-ion battery positive active material, each second battery unit independently comprises a sodium-ion battery positive active material;
• a ratio of a number of the at least one second battery unit to a total number of the battery units is 1/3 to 2/3.