How often to charge battery? Can I use fish finder indicator?

[Ki Ki]

So, we have a new to us boat. The battery is used for cranking and the fish finder, amongst a few other items. Any idea on how often we need to charge the battery before going out?

Our Humminbird fish finder has a low battery indicator warning on it. Can I turn that on while it's out of the water to check the current reading? Last time while running it said it was at 13.5. What's the minimum I'd want that to say before taking it out?

 

[briangcc]

Re: How often to charge battery? Can I use fish finder indicator?

Going to need some more information from you before that can be answered. Year/Make of boat, Year/Make of motor, size of battery.


Generally speaking, I leave my battery on trickle charge over the winter, leave the battery hooked up over the summer, use my fish finder for several hours on end, and have yet to deplete my battery during a normal season. But I have an alternator for my 5.0L FI Volvo so that charges the battery when I'm running between fishing spots.

I doubt you'd run down your main battery enough to warrant a charge during a normal day out fishing. Now tack a trolling motor into that equation and you'll need to be worried about how quickly it'll drain. Or leave it on overnight without starting your main engine to charge your battery and you could run into issues.

 

[NYBo]

Re: How often to charge battery? Can I use fish finder indicator?

You have a small outboard, IIRC, with a very limited charging capacity. Therefore you should throw the battery on the charger AFTER every outing (don't let it sit partially discharged between trips). You may find that you run the motor enough to replace the modest amout of juice you use, but charging each time eliminates the guesswork.

A fully charged battery will settle at 12.6v.

 

[Chris1956]

Re: How often to charge battery? Can I use fish finder indicator?

12V lead acid batteries don't change their discharge voltage in a linear fashion. They will read 12V until severely run down. Unles the battery is a deep cycle type, you do not want to run it down. I recommend you charge it every night, after use.

 

[bruceb58]

Re: How often to charge battery? Can I use fish finder indicator?

12V lead acid batteries don't change their discharge voltage in a linear fashion. They will read 12V until severely run down.

Actually, the opposite is true. They discharge linearly. 12.6V is fully charged. 12.0V is close to the 50% point.

You want to measure the voltage when the battery has not been charging for 30 minutes so that the surface charge dissipates.

 

[H20Rat]

Re: How often to charge battery? Can I use fish finder indicator?

Actually, the opposite is true. They discharge linearly. 12.6V is fully charged. 12.0V is close to the 50% point.

You want to measure the voltage when the battery has not been charging for 30 minutes so that the surface charge dissipates.

10-4. For the most part lead acid's are pretty linear. From the OP's use though, unless you have a trolling motor, the fish finder draws next to nothing. I've left mine on for 48+ hours before and the boat started fine. A small outboard will have more than enough charging capability to recover what the fishfinder draws in normal usage.

The different lines on the graph indicate different loads, so for a fish finder, look at the top one, discharges in longer than 8 hours. 12.00 volts puts you at about 65% discharged, which is bad for a starting battery and not great for a deep cycle, I wouldn't go lower.

Long story short, if its only a fish finder, just go fishing and don't worry about your battery!

 

[ThrottleBack]

Re: How often to charge battery? Can I use fish finder indicator?

I don't have an alternator so when I get home my first move after parking and securing the boat is to put the battery on my float charger. It stays on till the next time I prep the boat to leave. If you do not have a float charger i strongly suggest one. I have several of the $29 ones from Walmart and they are great.

 

[Chris1956]

Re: How often to charge battery? Can I use fish finder indicator?

So you consider a .5V drop when the battery is 50% discharged to be a linear relationship? On a lot of voltmeters .5V fluctuation is the error term.

 

[Ki Ki]

Re: How often to charge battery? Can I use fish finder indicator?

I don't have an alternator so when I get home my first move after parking and securing the boat is to put the battery on my float charger. It stays on till the next time I prep the boat to leave. If you do not have a float charger i strongly suggest one. I have several of the $29 ones from Walmart and they are great.

Wow, very helpful info all!

Here's another question. Do you find that it works best to leave the charger on manual or automatic for an overnight charge? Mine has started both times out, but it couldn't hurt it throwing on 'automatic' charge could it?

 

[bruceb58]

Re: How often to charge battery? Can I use fish finder indicator?

So you consider a .5V drop when the battery is 50% discharged to be a linear relationship? On a lot of voltmeters .5V fluctuation is the error term.

Yes it is a linear relationship during the discharge from 100% to 80%. Take a look at any flooded acid battery discharge curve including the one that smokingcrater posted. Can't get much more linear than that one.

If your meter has a 0.5V possible error, you need to buy a different meter. The meter I use has an accuracy of 0.3%. On a 20V scale that equates to 0.06V. 0.5V would be 2.5%. Even a $5 meter can do 1%.

 

[NYBo]

Re: How often to charge battery? Can I use fish finder indicator?

Wow, very helpful info all!

Here's another question. Do you find that it works best to leave the charger on manual or automatic for an overnight charge? Mine has started both times out, but it couldn't hurt it throwing on 'automatic' charge could it?

Automatic.

And yes, you can use the voltage readout on the Humminbird at any time to check the state of charge. I did that just yesterday on mine, as a matter of fact.

 

[Home Cookin']

Re: How often to charge battery? Can I use fish finder indicator?

a lot depends on the motor's size. I don't see charging a battery before every use, but there may be unusual circumstances that would warrant that unusual procedure. And the smaller the motor, the less the recharge.

My fish finder also has a low battery alarm but does not give readings. I drift with the FF and VHF on, and often when I start the motor it beeps. A couple times, hot day and long drift, it has beeped without my doing anything. But in either case, the battery has had no hesitation whatsoever in turning over the 150 2 stroke. Therefore, what might worry some, merely annoys me.

I have two batteries in the boat with a 150. If yours is 25hp or less, you can always pull start in the unlikely event the FF wears the battery down so low it won't turn over and start a warmed-up motor.

 

[ThrottleBack]

Re: How often to charge battery? Can I use fish finder indicator?

Wow, very helpful info all!

Here's another question. Do you find that it works best to leave the charger on manual or automatic for an overnight charge? Mine has started both times out, but it couldn't hurt it throwing on 'automatic' charge could it?

The unit I'm using only has automatic. Just hook it up, plug it in, walk away. It will charge to full then go into "float". Float means that the battery is charged and if it begins too loose any juice the charger will automatically kick back on then float again. I have this one, several of them. One is on my motorcycle, one is on my kids ATV, one is on my boat, and another is set up on a chain of power wheel batteries. No dead batteries in this house lol.

I stand corrected, they are 19.99 i couldn't remember.

Schumacher XM1-5 1.5 Amp Fully Automatic Power Charger and Maintainer, Microprocessor Controlled Battery Charger, Automotive Battery Charger, Battery Charger Maintainer

 

[MH Hawker]

Re: How often to charge battery? Can I use fish finder indicator?

This should help you out.

 

[crabby captain john]

Re: How often to charge battery? Can I use fish finder indicator?

I have 2 batteries and a 150 Yamaha 4 stroke. The boat is used every week at least once (except for 1 month in winter when I vacation). often it is used 2 - 4 times. Sometimes troll, other times drift or anchor with the motor off. The terminals are kept clean. Each trip alternates batteries. The VHF and FF GPS are always on. Never had a low battery and never put a charger on one either. The Yamaha gage shows battery level as long as the key is on,,, never a problem seen.

 

[Chris1956]

Re: How often to charge battery? Can I use fish finder indicator?

Do you guys understand linear? According to Smoking Crators graph, a 20% voltage drop equates to a 100% discharge rate. How is that linear? Linear would be that a 50% charged battery would have about 6 volts.

You can up-size the horizontal axis all you want, but the relationship is not linear.

I had a $10 VOM. I found out that it could not tell the difference between 400 ohms of resistance and a dead short. I tossed it out and bought a $50 meter. Not sure the average boater would be able to measure voltage within 1/2 volt accurately, with the equipment he is willing to buy, so his error rate could be 20%.

The practical answer is to charge the battery each night. It makes no sense to do anything else.

 

[bruceb58]

Re: How often to charge battery? Can I use fish finder indicator?

Do you guys understand linear?

I am an Electrical Engineer. I think I know what linear means!

In engineering, devices are often described as operating in their linear region. That's all we are discussing here.

In the region of interest between 0% and 80% its linear. I agree that last 20% isn't linear but if you want to figure how depleted your battery is in the range that most people discharge their batteries, its very linear.

If you bought a meter that can't tell the difference between 0 and 400 ohms, that is either a pretty pathetic meter or there is operator error. I am beginning to think the latter.

If you want to spend a whopping $19 on a meter:
http://www.sears.com/craftsman-mult...p-03482141000P?prdNo=1&blockNo=1&blockType=G1
You will get one that measures to 0.5%. @12V that's 0.06V error. Plenty of resolution to figure out where you are on the discharge curve.

 

[MH Hawker]

Re: How often to charge battery? Can I use fish finder indicator?

this could be interesting opcorn:

 

[bruceb58]

Re: How often to charge battery? Can I use fish finder indicator?

this could be interesting opcorn:

Or he could just read your table...his choice.

 

[Chris1956]

Re: How often to charge battery? Can I use fish finder indicator?

Bruce, A voltage drop of 1.5V out of 12.5V ( about 12%) that equals an 80% discharge is linear? I am a System Engineer, and that makes no sense to me. I can adjust the scale to make it look like the discharge line is at a 45* angle. Any idiot who took Stats can do that, and do it within the rules. But as they say, there are liars, Damn Liars and then there is statistics.

I also know how to read a VOM. I was real surprized to discover the inaccuracy of the meter. I never expected to find that kind of inacuracy, even in an inexpensive meter. I was troubleshooting the fuel injection on my car. It had an 80 pin PCB that controlled the FI with resistance and voltage specs for each pin pair. When I didn't belive the resistance measurement on a pair of pins, I dragged out my old Simpson Meter. Repeating the test with the Simpson, I found that the proper 400 ohm resistance spec on the pair of pins.