Another Battery ?

With the starting / Cranking battery connected directly to your motor you would think if the motor’s Alternator is working correctly ( I think mine is ) that your battery should always be near fully charged. Whenever I hook the charger to my starting battery it seems like it takes way longer to get it to read fully charged than it should. Its been this way with both my last starting battery and my new starting battery. I can charger 2 fully discharged trolling motor batteries in less time than I can charge what should be near a full charged cranking battery. Why is this? I do run 2 graphs off of the cranking battery as well and sometimes the livewell but I’d not think they would use much power. I do a fair amount of running the big motor ( 150HP ) so id think the alternator would be putting out lots of charge to the battery while running. The battery has never failed to start or run the electronics so that’s not the problem. Just curious why it takes so long to charge. I know some fishermen who say they never charge their starting battery.

My guess is that it’s difficult for the voltage regulator on the motor to maintain a precise voltage for a 100% charge. Your charger will provide a very precise voltage at a very low amperage. Your motor at wot is pumping in a very noisy voltage at nearly 50 amps. Hence the term “trickle charger”. I’m sure someone can provide a better explanation.

I have a similar setup. I have 3 batteries, 2 solely dedicated to the trolling motor and 1 dedicated to starting the outboard, 2 screens, pumps, lights, and the talon. All three batteries are equipped with on-board chargers. I don’t usually run my outboard for long periods of time, however. But then again, I don’t fish for long periods of time either so I don’t burn a lot of power out of my batteries.

When I get home, I usually hook them up to fully re-charge and they are all fully charged usually within an hour. Every once in a while I’ll hook up a trickle charger directly to the batteries to do a low-volt reboot.

I should indicate I’m on year 4 of this current battery set.

If your worried about the single battery losing juice, you could put a jump starter in your boat. I keep one in my truck in the event I need a jump but having one in the boat makes sense too.

fishthumper wrote:

With the starting / Cranking battery connected directly to your motor you would think if the motor’s Alternator is working correctly ( I think mine is ) that your battery should always be near fully charged. Whenever I hook the charger to my starting battery it seems like it takes way longer to get it to read fully charged than it should. Its been this way with both my last starting battery and my new starting battery. I can charger 2 fully discharged trolling motor batteries in less time than I can charge what should be near a full charged cranking battery. Why is this?

Do some basic diagnostics and you’ll have the answer.

Bring a multimeter along on your next trip to a lake or run the motor on water muffs or hose connection in your driveway.

Take a voltage reading off the starting battery BEFORE starting the motor.

Then take a reading with the engine running at idle.

You should have 12.6 (with a small +/- factor of .x) volts before starting. Then at idle, you should read something between 13.5 and 14.5 volts, again with a small .x +/- factor if your alternator is working properly.

So that will tell you if your alternator is working.

Next question: Do you have a master cutoff switch on your starting battery?

If not, the likely answer to “why does my starting battery always take a charge” is that all the little brain boxes in all your electronics are eating away at your battery. Install a marine master cutoff switch on your battery and put a stop to that by throwing the cutoff switch when you get home after each outing.

It is possible that you have a short somewhere in the system that is eating away at your battery. Generally, if this is the case though, your battery will run completely dead in a matter of a few days. I don’t think this is your issue but wanted to bring it up as a possibility if all else should fail.

Grouse

If you troll a lot that is your issue. I had same problem look up specs on your motor. Fuel injection system draws more amps at low idle then generator produces. Unless your on a big lake to crank it up for a while a two minute WOT trip back to landing don’t make up for a few hours of trolling.

Some Power steering systems will also cause a negative draw also. Big motor alternator can’t keep up.

All excellent Ideas. I know the master shut off switch is the best Idea. I need to get one of those installed.

I did check the voltage while the motor was running and that confirmed that the alternator is working fine.

You could do this to confirm either a draw when not in use or battery issue.

Disconnect battery. Charge full. Let sit for a few days. See if still fully charged after sitting. If still fully charged, confirm draw. Hook up battery, let sit for a few days. If it needs a charge, you need a master shut off switch. That or just leave it on the charger when ever not in use.

You didn’t mention if you had an on board charger. These typically go into a maint mode after the charge cycle. Plug in and forget about it.

-J.

The batteries for the trolling motor connected to a onboard charger. The cranking battery is not. I use a manual charger to charge the cranking battery.

Buy a 1 bank charger , 6-9 amp !

To give you a idea of how long the cranking battery is taking to charge. I put the charger on it this morning around 8:00 and set the charge to 10 amp. When I got home from work at around 3:30 it was still charging and not reading fully charged. That seems like a long time to get the cranking battery back to a full charge. I had it at a full charge a few weeks ago. And have only been out fishing once since then. I think I need to put a master cutoff switch on it. Another thing I dislike about this cranking battery is it doesn’t have post. It makes connecting the manual charger a little more challenging. Hard to get the clamps onto the top of the bolt used to hold the connections

huskerdu wrote:

Buy a 1 bank charger , 6-9 amp !

How will a 1 bank charger be any different than using the manual charger I’m currently using. I can set the manual one to 15, 10 or 2 amp charge. My next boat will have a onboard charger hooked to all the batteries on the boat. Until then I don’t see any value in installing a one bank charger. A location to mount it would also be a issue. I had a hard enough time just getting the bigger cranking battery into the area designed for it. No chance of also getting a one bank charger in there as well.

Could be your charger.

My 300 HPDI would have issues starting when I ran my electronics for extended time, several times I had to start the big motor by changing or jumping off the bow mount motor batts. I now have 2 12v batteries hooked up in series that I use for the starting motors and my running my electronics.
I had a four bank charger installed to charge the 36V trolling motor batteries and connected bank 4 to the two 12v batteries.

Have not had any issues since.

jeff_huberty wrote:

My 300 HPDI would have issues starting when I ran my electronics for extended time, several times I had to start the big motor by changing or jumping off the bow mount motor batts. I now have 2 12v batteries hooked up in series that I use for the starting motors and my running my electronics.
I had a four bank charger installed to charge the 36V trolling motor batteries and connected bank 4 to the two 12v batteries.

Have not had any issues since.

You mean parallel. Series would create a 24v system.
I know you know. Just clarifying for anyone reading

Dusty Gesinger wrote:

Could be your charger.

Verify that also if you haven’t already. I have a charger that can never seem to top off any battery I put it on. I know it’s something wrong in the charger as I can use a different one and no issues topping off the same battery in far less time (equal amperage).

FishBlood&RiverMud wrote:

You mean parallel. Series would create a 24v system.
I know you know. Just clarifying for anyone reading

Bingo

I did not see the age of your starting battery? Batteries do weird things sometimes when they start to go bad. Get your self a good automatic 12v charger that senses when the battery if full and switches to trickle charging.

The cracking battery is new this spring – Its a AGM battery.
The manual charger is a fully automatic one.
I know the charger it is working correctly because it has charged this and other battery to full charge recently.

Jon Jordan wrote:

You could do this to confirm either a draw when not in use or battery issue.

Disconnect battery. Charge full. Let sit for a few days. See if still fully charged after sitting. If still fully charged, confirm draw. Hook up battery, let sit for a few days. If it needs a charge, you need a master shut off switch. That or just leave it on the charger when ever not in use.

You didn’t mention if you had an on board charger. These typically go into a maint mode after the charge cycle. Plug in and forget about it.

-J.

Check this first I have had 3 brand new Deka batteries in my Jeep Grand Cherokee go bad in the last 18 months. Sits for three days and would not start.

Merc ( edit to add,I am assuming it is a merc?) has had some problems with their alternators in the past.
I would take it to a dealer or reputable independent shop and have the alternator tested for AC output of two milliamps and above.
what happens is the diode or rectifier is very cheaply built and doesnt work correctly or has failed prematurely.
AC voltage in even tiny amounts will cook a DC battery but wont affect the electronics unless it becomes too high then it will start frying electronics.
the only reason it doesnt at low output is because the battery will absorb it for a while.
I have seen where when this happens,batteries become very difficult if not impossible to charge to full rate because the plates have been eaten away.

I tried reading what brand of battery you are using but didnt see it??

Some chargers are battery type specific, wet cell vs. AGM. You said that your battery is a new AGM, do you have the charger set to AGM?

Take the battery back? Get it tested. Get alternator tested sounds good too. I had Interstate batteries for my State vehicle when I worked and had to get a new one every 3- 6 months for some reason. There are only 3-4 battery makers I believe but the retailers all put their own name on them so it seems like there is a big choice.

But, just because you have a battery bank charger or being charged from the motor according to the gauge in the dash doesn’t mean the battery is charging at all or properly or holding a charge we know that.
My solution excluding trolling batteries, was one battery dedicated to cranking and one for accessories or a “house”battery separated with a Blue Sea battery separator/switch. Not a Perko. Plenty of videos on them.

Lastly, I installed a quality battery gauge that shows the actual charge amount of the battery by Pro Charging Systems Made in USA and the free DeltaView Link smartphone app.If I”m out all day with the radio on or at night with the lights on I know how much energy is left in the batteries. Takes the mystery out of it. Once you’ve been stranded with a dead battery you won’t want it to happen again.
My 3 cents. Installed on a 2 year old Alumacraft. More info I posted in the Alumacraft Group. Good luck.

A fully automatic manual charger? Put the charger on your car and see what it does