I just have to clarify things a bit as some might be confused still with the terminology. A battery maintainer is as stated and a trickle charge does also as stated. But the CTEK and Battery TENDER (branded) (expensive one) for example are conditioners as well.
Battery tenders yes they will monitor and charge if the voltage drops below a threshold to maintain the state of charge. Battery trickle chargers will put a small charge (minimum) most of the time to maintain the voltage with slight variations.
Battery conditioners (which are misnomered as battery tenders) will in fact (as used for deep cycle marine batteries as example) are designed to both charge and lightly discharge the battery in a cycle (just like it would if running the vehicle) to maintain it's top performance and extend the useful life of that energy storage device.
Having a charger that can do both (or multi function) is beneficial as it keeps the reactions in the cells so sulfation doesn't happen as easily. Also an overcharged battery or cell will discharge some of the gases (acid mist) in the process and actually weaken the battery as it gets warm from the infusion of constant energy. A 1 AMP trickle charge on a large car battery or marine battery over a winter season for example (4-5 months) likely won't cause any real issues. But a 2A trickle charge on a small battery (bike/atv etc) has more effect and can shorten the life span. By as much as half. So no you won't notice it this year or maybe even in 3 but it does have an adverse effect. But the expensive ones (as noted prior) will help to maintain the life span of those smaller batteries and are for long term storage the absolute preferred method...
Infact I'd rather (and have where no power) disconnect the negative terminal and leave a healthy battery in the vehicle for a few months then put it on a small cheap "trickle charger" as it will last longer..and in almost every case started right up next spring...but key is to disconnect it from the circuit so no possible drain...a healthy battery won't discharge much on it's own if no draw against it unless it was already ready to be replaced!!
Built many batteries with Prestolite etc and recovered lots of "dead" ones that were fine....sorry if this was long winded...but there are 3 functions and distinction should be made for clarification if shopping for one for your vehicles/toys.