onboard battery chargers

[lakermaker]

I don't know much about onboard chargers, are these only used when at the dock and plugged into the dock electric hookups or can they actually charge a second or third battery that is not being used when the boat is going? Would appreciate any info about their workings. Thanks

[bc22]

got at least 2 batts? gotta have a batt. charger to maintain those to optimal condition and maximize the batt life. you can get a "on board" unit (with or without fancy mounted plug-in outlets for easy charging when 110v is available or a portable unit w/ alligator clips.)
on board chargers require 110v and therefore are "shore power" items.
if you what 'underway' charging; your alternator set up will charge batts. if set up right.
with dual batts., make sure at least one is dedicated to starting and not for running aux. items like downriggers, lights, pumps, electronics., etc.