I want to make a solar charger for tool batteries. I'm thinking plug a standard AC dual 5 amp 20v battery charger into an inverter charged via a solar battery bank. Enough to charge four batteries during the day. That's not in the budget so I'm going to start small with just one battery at a time (600watts?). Maybe two batteries a day if I can afford it.

Who here has built such a battery bank? What advice do you have? What handy online calculators do you recommend? Is there a spreadsheet available that is better than a calculator? In the past I would have looked for those myself but search engines are totally useless now. Would you rather have one big battery hooked up to the inverter or a bank of smaller batteries in series or parallel?