My Prolong system from Hybrid
My Prolong system from Hybrid Automotive was $700. I was able to nurse my failing battery for 2 years/20,000 miles with their system (grid charger and automatic voltage cut-off discharger.) Now I've just put a new battery in and I can use it to balance the battery when needed (in 3 years or so) Not Snake Oil. Worth it for Insights, for sure.