Thank you for your interest in Sump Pumps Direct. Per the Liberty 441 Owners Manual:
Use of a standard automobile battery, GEL type, or a Maintenance Free (sealed) battery with this charger is not recommended.
An automobile battery may require charging after only 1-2 hours of continuous use, and the repeated charging cycles may cause early plate failure in the battery.
GEL-type batteries require a lower voltage than the charger is designed for; they may overcharge.
Maintenance-free (sealed) batteries require a higher voltage; they
may never reach full charge.