Lead Acid Battery Life Expectency

Lead acid batteries hate to be discharged.

They especially hate it when you drain them completely. Your battery should come with a datasheet that details the life expectancy vs. the discharge current. This will let you estimate how long your batteries are likely to last based on how much you're going to use them.

Different types of batteries have different lifespans. High cycle batteries may only last a few hundred cycles if you use them with an inverter system.

This is the graph for the batteries I have at home (Stride 100Ah Solar)

So if I drain them completely each time I use them, I can expect 300 cycles (or load-sheds) from them before they give out, defined as when the battery only holds 60% of the original capacity.

I'm drawing roughly 100W per battery for 2 hours at a time, so that's 200Wh, or 20Ah per 12V battery rounded off (There's no point working accurately here because these are rough estimates). The batteries hold 100Ah in total, so I expect to use 20% capacity per load shed.

I estimate that I'll get about 2000 cycles based on 20% usage. Even if I get load-shed every day then the batteries should be good for 5 years.

Even without load-shedding, don't expect low-end batteries to last much past 5 years though.