We used to do it ourselves 50 years ago when parts were expensive and labor was cheap. I wouldn't even think of doing it any more. I buy batteries with a 3 year free replacement and make sure they go dead within 3 years. If a battery is completely discharged and allowed to set a couple of weeks, it will now longer take charge. We have the same type of computer tester in our shop that the battery sellers use. I make sure they show dead and get a new one for free. This is the cheapest way I know of to keep good batteries in our welders, forklifts and my old jalopies.