To figure out the battery requirement, you need to know the following: 1. How many watts the solar panel can produce 2. The amount of power you will provide to the inverter 3. How long you need to draw power from the inverter 4. The inverter efficiency 5. The battery depth of discharge. The inverter load and duration play a huge role in determining battery capacity. The inverter load determines the battery discharge rate. The larger the inverter load, the faster the battery will discharge.If you are running a lot of devices simultaneously it will. Technically a 300W solar panel is enough, but for optimum results you need way more.Six 300W solar panels is sufficient to run all your loads for. The amount of time you need to draw the current determines the battery discharge rate. Let's say you get 1500W of sunlight from your 300W solar panel (ideal weather). A 125ah battery will draw 1500W for an hour. A 6.5ah battery is enough for 1500W for 30. It is possible to overcharge solar batteries, but it is unlikely. The only way this can occur is if you connect the solar panel directly to the battery. That exposes the battery to possible.