Wow......I've heard some really bad advice here. Not all batteries are the same, even within the same chemistry family. Yes, an amp is an amp and a volt is a volt, but the amp hour rating is not always the same. It depends on the rating test used. The construction of lead/acid batteries can be very different. Different constructions exist because each construction has its own attributes. Traction motor batteries use thick lead plates and are amp/hour tested at nominal usage current over a 6 hour limit. Marine batteries, although also classified as deep cycle, are tested over a 24 hour low amperage discharge rate. High discharge rate, automotive type batteries use a very thin folded fabric reinforced plate construction reflecting the high surface area requirement to support a several hundred amp high discharge rate. Functionally, ion migration from the plates is only available from the plate surface. It takes time for the charged ions to migrate from inside the plate to be available for discharge at the surface, so the surface area to plate depth ratio is tailored for a given usage. Battery usage outside its design envelope will cause a much shortened life span. A good rule of thumb is the charge rate should optimally not exceed 10% of its amp/hour rating. Slower charging is not an issue, but faster is. So, using a forklift battery charger on a stack of marine batteries may very well exceed the maximum charge rate of the marine batteries.
Many of you think that lead/acid batteries are not as good as say other more modern battery chemistries like Lithium Phosphate. You could not be more incorrect. LiPo batteries are very temperature sensitive and their performance really falls off below 10* C. Lead/Acid batteries can work well at -20C. Every battery chemistry requires its own charger tailored to that chemistry.......never mix the chargers.
So, yeah, you can misuse batteries, as advised by others in this thread, but you're only fooling yourself.