However, todays renewable energy batteries are better than ever, and so are the devices that regulate and protect them. Follow these guidelines to avoid the vast majority of all battery problems. Energy use in most home power systems increases over time, so consider sizing larger than that. After 1 year of service, it is NOT advisable to enlarge a battery bank by adding new batteries to it, because batteries' voltage response changes with age.
Stray currents flow, causing losses and failure to equalize.
Luckily, a PV array can be expanded at any time. Good deep-cycle batteries can be expected to last for 5 to 15 years, and sometimes more. Cheap batteries can give you trouble in half that time. Buy from a reputable source. The ideal battery bank is the simplest, consisting of a single series of cells that are sized for the job.