I think the mixed results on battery life with cheap trickle chargers has to due with their inconcistent and sometimes crazy voltage variations seen during operation. Not all, but most cheap battery maintainers cause more harm than good. However, if you use a quality charger like the BatteryMINDer brand you can leave it connected indefinitely without the maintainer causing trouble. Unfortunately these are in the $240 range. I attended an IA seminar last weekend and we had a Concorde Battery factory rep give a presentation and he said their testing showed these BatteryMINDers had perfect voltage control across all charging scenarios with the added benefit of a desulfating feature to extend battery life and help bring back whacked batteries. None of the competition could compare.
I have two of these high dollar units, 14V each, one labeled for Concorde batteries and one labeled for Odyssey/Hawker batteries. So the Concorde guy made me feel a lot better about the investment. Since each BaterryMINDer model is brand specific and voltage specific (14 or 28) and type specific (AGM/RG/Wet Cell) ot can hit it's specific manufacturer's charge recommendations exactly. The down side is that not only are each individually expensive, but if you deal with multiple aircraft with different batteries the cost of having one of each type is prohibitive.
On the bright side an Odyssey PC680 combined with one of these chargers is still less expensive than an EarthX set up. Not that I think EarthX batteries aren't worth it. I have an EarthX EXT900-VNT in my RV-8 and love it. But then it too requires a trick Optimate Lithium charger/maintainer.