This device works as a battery charger and maintainer and is ideal for a wide assortment of battery types and sizes. Nexpow F1000 1A Battery Charger, $20 (was $65) at Walmart.

This battery charger can charge all types of 6.0-volt and 12.0-volt lead-acid batteries including AGM, GEL, WET, maintenance-free, calcium, lithium-ion, automotive, marine, and enhanced flooded ...