been down that road with my rv.
if it is a decent charger, it takes awhile for it to sense the battery and if it is a three stage, it needs to be connected all the time. on my rv, the deep cycle battery was actually bad but tested good, hummm, go figure. anywho, it would boil the battery even with 1.5 amp so the timer and yep, sailed in your boat. a new battery and the charger is working fine.
hf does make a three stage charger that is sealed for marine use and so far, seems to be working. i have a tow truck that does not run much, 40k miles since 2005 so it stays on a charger.

https://www.harborfreight.com/15-amp...ner-99857.html

 

I use a Battery Tender and have it on a timer to charge for two hours a day from 01:00 to 03:00 hrs.
No issues.
Had to replace the original 2012 battery last September.

 

Get yourself a good quality tender, which you can leave permanently plugged in. They monitor your battery, fully charge it, then maintain a full charge by waking up every now and then to give your battery a hug and a feed. I've been using them for umpteen years!

 

Invest in a battery tender and just leave it plugged in all the time....will not harm your battery.

 

Let me reiterate what has been posted before me ... B A T T E R Y T E N D E R and forget it

 

What's the point in putting it on a timer? You are not saving any money. These things take so little power you could run one for years for a couple bucks. The timer itself probably uses more power than you are saving on the tender.

Seriously interested in what's the reason for the timer. Maybe something I'm not understanding. thx

 

 

There is nothing wrong with your thinking of running a standard charger for fifteen minutes per day. Unfortunately at some point the battery may become fully charged and the standard charger won't know. It is at this point that your battery slowly boils.
This is where the new chargers save your battery as they are designed to stay connected as previous posters have pointed out.
I have the HD one which is made I suspect by Battery Tender. You can get Optimizer or C-Tek which are more powerful to recondition and charge a flat battery before going into tender mode if required.

 

well to answer your ?.
no it will not back feed, if it did, you would instantly know.
old style transformer types used a rectifier that made dc from ac and if the rectifier opened, no charge current, if shorted, smoke and blown fuse.
newer types use rectifier with transistor or other semi-conductor technology, same end results.
even newer, switch mode or high hz charger, same end result.
you can't get cheaper than schumacher from wally world, been using them on my mc's forever. not that they are fantastic, just local and easy to get, lawn equip the same.
i am trying the hf unit on my tow truck, why, hermetically sealed and in engine bay actually mounted on alternator bracket.