When it comes to flooded cell Lead Acid batteries, read 'maintenance free' in the advertising as 'unmaintainable'. In cyclic use they NEED an equalizing charge at somewhat regular intervals, which involves overcharging till the cells are gassing sufficiently to stir the electrolyte, sampling the S.G. periodically until it stops rising significantly in all cells, then topping up with distilled water to the correct level. Obviously you cant measure the individual cell S.G.s of a sealed battery, so the best you can do is a timed equalizing charge, but the reserve electrolyte capacity is minimal and you cant top up the cells, so the total cumulative time you can equalize for before the electrolyte level is down to the plates is very limited so the service life is likely to be significantly shorter than a comparable battery with removable caps. Also with no caps to remove to allow the hydrogen to freely escape, the equalizing charge fills the battery's cell headspaces and vent passages with a highly explosive hydrogen/oxygen mixture, so you are one spark (e.g. from a cracked link) away from a nasty explosion.
A good quality flooded Lead Acid battery with removable cell caps, properly charged, regularly maintained and not deep discharged for significant periods should be good for a service life of five to seven years, assuming its of the correct type for the application, with sufficient capacity to have an adequate reserve so the reduced capacity towards the end of its life isn't problematic.