The invention discloses a composite battery. The composite battery comprises at least one lead-acid battery pack and at least one lithium ion battery pack connected in parallel with the lead-acid battery pack, wherein single lead-acid batteries in the lead-acid battery pack have electrolytes with the density of 1.29-1.33g / ml, and / or, the positive poles / negative poles of single lithium ion batteries in the lithium ion battery pack contain an active substance, the active substance at the positive poles of the single lithium ion batteries is at least one of lithium iron phosphate, lithium manganate, lithium cobalt oxide, a ternary material and the like, and the active substance at the negative poles is at least one of graphite, mesocarbon microbeads, lithium titanate and the like; and the proportion of the total open-circuit voltage of branch circuits of the lead-acid battery pack and that of branch circuits of the lithium ion battery pack is 0.99-1.01:1. By adopting the composite battery provided by the invention, the total open-circuit voltage of the lithium ion battery pack is matched with that of the lead-acid battery pack, so that the lead-acid batteries are prevented from damage, and the service life of the lead-acid batteries is prolonged; and meanwhile, the composite battery has the advantages of simple structure, easiness in implementation and low cost.