Mixing strings of Lithium-Ion and Lead-Acid in parallel

Abstract: The purpose of this survey has been to test and analyse the behaviour of battery systems mixing parallel strings of lithium and lead acid. The underlying theory of why batteries of different chemistries behaves together was investigated in order to understand the resulting tests. Several tests were made with different products, loads and chargers in order to confirm this theory and to discover cases where the system works good and where it works bad. Based on this understanding a script was made in order to find a point of the least annual cost. Annual cost was then compared with systems of Lead acid only and Lithium only. The final goal for the script was so that a salesman can input known parameters for a backup site. Script is then adding a small Lithium battery in parallel with a fixed Lead acid battery and, increasing Lithium in size and estimating depth of discharge for Lithium and Lead acid at each step, until desired breakpoint. A point of minimum system cost together with Li size is then represented together with the recommended current limits.