batteries

[rvsalesman]

am planning on replacing batteries this year, will start with 3, then the other 3 4-5 weeks after. any major drawbacks to this plan

[Larry1950]

It could cause undo stress on the new batteries, as the new batteries would have to make up for what the old batteries can't. You would be better off to change out all the batteries at one time.
How old are the old batteries? Is the water level good? Did you check the cells with a hydrometer?