Understanding the key factors that affects overall performances of a battery is crucial to the lithium-ion battery industry. To this end characterisation methods must be specific, reproducible and representative. As such, an interference free and reproducible analytical method with a low detection limit (50 ppb) to evaluate manganese dissolution from lithium-ion battery positive electrodes is presented. Two different electrolytes (1.0 M LiClO4 and 1.0 M LiPF6 in EC:DMC (1:1)), LiFePO4, two nominally similar LiFe0.3Mn0.7PO4 samples and spinel LiMn2O4 are used for proof of concept. Mn and Fe quantification is performed on material ageing in solely in electrolyte, as well as, in a battery system with and without forced oxidation. It is demonstrated that water and free acid content in the electrolyte, as well as, imposing an oxidative electrochemical potential has a profound effect on manganese based material dissolution and battery performance.