"Many battery manufacturers do not recommend long term ( months at a
time) trickle charging. If trickle charging is used then the charge
rate should be very low or only intermittent. The best smart chargers
will only send an occasional pulse charge to the battery once it is
charged. They do not apply a continuous low rate of charge. Some
battery resellers state that applying a continuous trickle charge of
about 1/10th the battery's capacity is not harmful. However, we have
not seen any battery manufacturer condone the practice."
per all-battery site.

I'd like to start using those cheap solar units to keep my fence
charger and my vehicles that I don't drive much charged up. Anyone
use them?