Ex battery hens are not a good idea for a beginner. First of all, they are being removed from the farm (usually at 80 weeks of age) as they are "spent" that is, they have rached the end of their peak laying life, and egg production will slow right down. they may lay soft eggs, or mis shapen eggs.
Exbats are also prone to illness because they have never been exposed to normal pathogens available in the average back garden. Due to the strain on their bodies they are also prone to problems with their egg laying mechanics, such as egg yolk peritonitis, caused by internal laying. Or egg binding, which can become a medical emergency.
Exbats can be very poorly feathered when they first leave the farm, and are often intorverted and scared of everything. Often ex bats will have had part of their top beak removed in an effort to curb cannibalism in the battery cages, this can lead to problems with eating pellets, and they lay need to be transitioned from an exbat crumb to normal layers pellets over a period of time.
Some people say that if half survive the first six months then they are doing well.
In reality, the philosophy of getting exbats is not to get a cheap source of good egg layers, but to enable the hens to experience what it is to be a chicken as much as possible in how ever many weeks or months they have off the farm. to be able to feel the weather on their backs, to be able to dig for creepy crawlies, and to have a good old dust bath - any eggs should be seen as an excellent bonus, but not expected.
For beginners I would recommend getting some POL (point of lay) hybrids. You will be able to get ISA browns/warrens, which are the hybrid used on commercial farms, and benefit from their superior egg laying ability without having to worry about the issues which come from ex bats... then down the line, once you are more experienced, you may still choose to get some exbats to give them a nice retirement