I've used the BatteryMinder from Northern Tools for years on my batteries over the winter. It pulses the battery to prevent the number one cause of battery death - sulfation.
https://www.northerntool.com/shop/tools/product_200332201_200332201 Full-time battery monitoring automatically tests battery continually, supplying only the current needed to maintain battery at full charge
8-stage unit charges and maintains from 1 to 4 batteries at a time (12V batteries parallel-connected or two 6V batteries series-connected. NOTE: Never connect 2 or more batteries together in parallel before fully charging each and checking their condition. Failure to fully charge each battery and check their condition can result in a serious safety hazard)
Does not overcharge, regardless of time connected
High-frequency pulses safely remove sulfate from battery's plates that prevent the batteries from holding a full charge
No need to add water to maintenance-type batteries during long, non-use storage