Boat battery charging time
 

For the first time I can remember the battery in my boat drained. I am guessing it is due to the bilge running for the couple weeks the boat had been sitting at the slip. I used a jump pack to get it going, ran it over to the island (10 minutes) where it sat for the weekend. Dead again Monday. Jumped it, brought it back to the slip (10 minutes), left bilge and everything off and found it dead again on Friday.

The battery was new at the start of the season last year. It's on a trickle charger now. Battery seems to test OK.

Before I worry too much about something drawing power (I have checked all the usual suspects), adding a back up battery or solar charger, I started thinking - once a battery on a boat is drained, how long does the boat have to run to fully charge it back up? I am guessing it takes a long time and the 10 minutes it ran did basically nothing to recharge the battery; my hope is that using the battery charger and bringing it back up to 100% will resolve the issue.

Anyone know how long a 90 HP Mercury outboard needs to run to fully charge up the battery?

I have to say those little portable jump packs are great - I keep one in each of my vehicles.

When I spoke to Nick last week (mentioned on another thread), he said that boat batteries essentially never get fully recharged through normal use because the last 10 percent or so takes hours to finish. That was why he said, for longevity, a trickle charger is essential.

The question now is whether your battery was damaged by being so discharged so long.

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10 min really isn’t enough, but it shouldn’t be stone dead the next time you use it.

Lead Acid batteries don’t like being left discharged.

I always disconnect battery for winter.

“Trickle charger” may not cut it. You want a “smart charger”. It can also tell you if the battery is any good when it’s done.

Chargers like these have brought batteries back that I thought were surely gone. My first battery lasted like 3 years. My 2nd battery (after buying a similar charger) lasted 14 years, and was still good when I sold the boat.

https://www.amazon.com/gp/product/B07CZG91FV

It’s also possible you have a leak in the boat. A crude old test I used to do was use a tail light bulb and put it in series with the (charged) battery connection. If it lights up, you have a significant leak.

But today I’d use an amp meter like this one. One of my favorite tools.

https://www.amazon.com/gp/product/B001TCWL1E

Thanks!
 

The battery had enough juice to power the trim and turn the bilge on, but not enough to start the boat (didn't turn over). It's on the charger now and once it's fully charged I'll test the battery.

The two weeks it was on the slip is the longest stretch it will sit all season. From now until October someone will be using the boat every couple of weeks. I am hoping the issue was rain which caused the bilge to run and drain the battery and the battery never got charged up enough to maintain itself.

Check the connections, make sure they are not corroded and tight. You need to put a regular charger on that battery to get it fully charged, then you can use the trickle.

I connected a battery charger and left it on all day. It showed the battery fully charged. Connections are clean and tight, the only switch I am leaving on is the automatic bilge. The jump pack if fully charged and in the boat. If its dead when I return I either have a bad battery or there is something drawing power.

Fingers crossed it starts right up when I need it!

A check can be made without meters or bulbs. This check must be made at night, in total darkness.

Hold the removed terminal clamp against the post you just removed it from. If there's a parasitic drain, tiny sparks will jump from the post to the terminal. It must be totally dark, so cover the working area (and your head) with a thick blanket. Keep flammables well away. :eek2:

Good point. It’s not a good idea to “trickle” charge a dead battery. Trickle is for maintaining, not charging.

LOL, sometimes you can hear the tiny sparks too :)

Even Interstate batteries are now lasting 1-3 yrs. Just changed one out under warranty. Less than one yr. old.

Hearing Sparks?
 

The tiny sparks I've got experience with couldn't be heard--only seen. Sparks you can hear indicate a major drain, not an overnight loss.

Also, keep the top of your battery clean. Loss of charge can travel across dust and dirt. Keep the rag you use. Watch accumulated acid eat holes through it after a few days! :eek:

correct.

under rating is as damaging as over rating.

charge rates at 15-25% of AH capacity is recommended. 10% is borderline. ie, 100ah , round numbers here, such as a group 31 deep cycle would rather be charged between 15-25amps than it would at 10 amps. Anything less will not only take forever, time-out a charger but will simply not be aggressive enough of a rate to prevent/break up sulfation

The answer to the original questions about how long to recharge a battery thats dead (assuming is is not more than 3 years old and/or has other problems) is that it will take hours of driving your boat to recharge it to a near full charge.

Outboard motors dont throw a lot of current, and what it generates must power all the electrical devices on the boat when its running.

AND, batteries dont charge in minutes, its hours.

The advice about a "smart charger is very good, they are much better then trickle chargers, but dont waste your money on a 1 amp or 2 amp model if you do many 10 minute runs in the boat, you will really need something more powerful.

ProMariner mages some good ones; https://www.overtons.com/promariner-...er-706694.html

Also the BatteryMINDer brand is really good and will extend the life of well used batterys better than most other brands; https://www.northerntool.com/shop/to...1886_200661886

Good luck!

As some have said your alternator is not designed to charge the battery. The battery is probably fine and needs to be recharged do it with a decent charger until fully charged. If you have a automatic bilge without some sort of trickle charger hooked up it will eventually drain the battery. If you don't have power to the area where your boat is located you may want to look into a solar charger.

Appreciate all the responses. As I said in the original post, first time I can remember a dead battery in a boat - and that goes back decades! Hopefully leaving it on the charger did the trick. I'll find out on Friday!

Spring launch
 

It's a habit of mine to check the batteries in the spring. I always find the batteries need water and a full charge. I use distilled water and fill to the rings, then charge the battery to full on a smart charger. Trouble-free for the summer!
This is when I find battery troubles such as the battery won't hold a charge, bulging battery, or corrosion around the post. The best time to take care of this is at the beginning of the season.

I *could* hear sparks from 1.5V AA battery. Maybe not today though ;(

I could hear sparks low enough on car battery that the drainage is “normal”.

I could hear it better than I could see it.

But again, an amp meter is the best because a little drainage is normal.

Also you can get a little inrush, like from charging caps in a radio that can be misleading. You want to see the settled current. And a little is common depending on the setup.

OUTSTANDING advice.

Address the cause, not the symptoms
 

First started reading this thread today. Lots of good info about batteries and chargers but little concern about what drained the battery, since this was a first. The OP mentioned rain, but surely there have been other deluges when the bilge pump ran and the boat still started. I'm reminded of two instances with similar symptoms (drained battery) on two different boats. In one, the grand kids were playing in the cuddy and left a light on. Not noticed until days later when: no start. Simple solution: turn off the master switch when the boat was not in use. Second instance: several weeks into the season, the boat sunk at the dock. We had been using it frequently, no problems. Then stopped using it for a couple of weeks. Turns out there was a leak in the bellows through hull. The bilge pump kept up when the boat was being used and mostly wasn't noticed as water ran to the stern and was pumped when under way. Changed oil a couple of times, new bellows. No other problems. Point is, it appears to me that the OP may not have a battery problem; replacing, charging the battery etc. may simply mask symptoms of another issue.

Again, outstanding advice.

Problem resolved, I hope
 

After charging the battery fully last weekend, I arrived on Friday night and the boat started without an issue.

My guess (and hope) is that the battery was never fully charged at the start of the season and it drained during the two week rainy period it sat on the slip. While the jump pack got it started, the battery did not get fully charged until I left it on the charger overnight.