I took my car off the road to save money but sometimes I need to transport large heavy items like a 60 pound flooded lead acid golf cart battery. Is there anything I can attach to my bike that can handle weight like that such as a cargo trailer? What about 2 batteries (120 pounds total)? What (if any) requirements are there to make this work? It is mostly flat where I live and my lowest gear is about 22 gear inches and I have 3x7 gears (21 speed). Thanks.
There are several options, you could make your own if you are the handy type. Or there are many ready to purchase from a local shop or online. Most of the ones that I see have a 120lb limit. So you would be close but probably fine as the max weight is generally higher than that listed for liabilities sake.
As for store bought option there are a lot of different companies that make trailers for bicycles both for hauling cargo, and touring applications as well as child carriers of course.
Here is one design just to give you an idea. The last time I saw a similar one in a shop I think it was about 200 bucks.
The type shown above attaches to the rear axle by way of that long arm at the front. Building one could be tricky if you don't have the proper tools and I imagine you would need to buy an axle intended for it.
If you want to go the DIY route, I found this write up that looked interesting and could be helpful.
The Burley Travoy looks like a great tool and one that I will personally be buying in the near future. you can see several videos of this product on You Tube , it looks very well made and practical in use as well as being quick to hook/un hook from your bike. Good luck with finding one that will suit, hope this helps.