Oldtimer

Rather than mess with the hard morning start thread, I wanted to respond to old-timer's opinion that a battery cutoff switch isn't necessary or advisable. I have enjoyed your analytical approach to problems but in this case my real world experience trumps stated current draw on an opti pro.
With a grp 31agm in good shape my battery charge would be lower than 70 percent in two weeks of sitting.
Before realizing the extent of draw I experienced two ruined batteries when the storage facility didn't charge as asked over winter.
After installation of switch... No draw and no problems. Granted a switch could fail but the fix is an easy do. Just my 3 cents
Bob

Unattended boat in a storage facility needs to have a cut off switch, or the battery cables disconnected for safety purposes, IMHO.

Seems that the usual group 31 battery claims a 125 ah capacity. That is it can provide 125 amps for one hour, or one amp for 125 hours.

You claim 2 weeks of sitting will deplete about 1/3 of that charge (less than 70% after sitting). That means you are somehow eating 40 ah over a two week period. which is 40 ah over 336 hours. Or roughly .12 amps per hour. That is one heck of a parasitic load. Certainly the motor is not doing that. First thing I would do is disconnect EVERYTHING from the positive post of the battery. Then take a digital voltmeter that measures amps to milliamps and connect it between the positive post and one wire at a time, making a note of parasitic drain for each wire. SOMETHING is pulling a lot of current.

I have five circuits on my boat. I will test them all tomorrow and report back with some numbers. 1 for the 200 pro xs, one for the dash, one for each of two hummingbird 998 / 958 depth finders. The last circuit doesn't count as it is the charger, but I would not be surprised to find it sucking a couple of ma.

BTW I am not of the opinion that is not necessary or advisable. I am of the opinion that it introduces a point of failure while attempting to solve a different problem (parasitic drain). If the parasitic drain is not a problem, then a cutoff is certainly something one can do without. Majority of existing boats don't have 'em. No boat I have owned had 'em. I would certainly agree that if your battery is really 1/3 discharged after two weeks it might be beneficial. Might be just as beneficial to disconnect for two weeks, then measure the remaining charge to make sure the battery itself is not the "problem".

For pure battery chemistry, I would prefer to always have a smart charger connected. Letting them self-discharge can drastically reduce their capacity unknowingly.

Savage: If I were storing remotely I would completely agree. Different topic however.

Drain IS the problem, but depending on how the boat, and its accessories are wired determines what the total draw will be. The figures for items in your boat/motor has nothing to do with what the draw may be on the OP's boat. For instance If the OP is powering his NMEA 2000 straight from the battery with no switch, but you have yours wired to a switch, then both boats could have very different draw totals.

Automatic bilge pumps are wired straight to the battery and are another source for battery drain. If your boat is outside with a leaky cover, or no cover, and it rains a lot, then the pump is going to run a lot.

Sometimes people leave devices on by accident.....The cut-off switch prevents the battery from using power when you don't want power used. If the switch fails it can be easily bypassed, but if the battery is dead.......it's dead.

Lastly, if the OP's battery is no longer going dead, after sitting, since the switch install........Then he DID have a draw, and his battery is then proven to be GOOD because it now has sufficient power after sitting for an extended period of time.

Probably the GPS antenna.

OK, I'll bite. HOW are we storing the boat? ON the water? On the trailer? On the trailer my bilge pump won't be a drain because it won't ever be turned on, and since the plug is only in when I am on the water, the bilge would drain before the switch would float anyway. He mentioned at a storage facility. Is it a lift and store or a trailer and store? Again, the latter would not need a bilge pump

I can't imagine electronics needing that kind of power, however.

If I were storing for months, the batteries would not be in the boat in the first place. A battery should not be left unattended for 90 days or more anyway, they self-discharge even when not connected to anything. For that length of time, I would take 'em home and keep them on a good maintenance charger

Again, just my $.02... Anyone is free to use whatever they want, this is a hobby for most.

And in closing, I would NOT power an NMEA or anything else directly off of the battery. That is beyond illogical to me as a computer person. Running off a battery, things need to be shut off, just as in an automobile.

There are automatic bilge pump devices, that are NOT a conventional float type switch.....

You have individuals from all walks of life wiring stuff up on boats..... you would not believe some of the hack jobs that I have seen. I just re-wired a ALUMINUM boat for a guy that installed his own electrical accessories without ANY FUSES.....a wire got pinched between some cross bracing and smoked a lot of wires. He was really lucky not to get hurt!

FYI. Storage was on trailer and inside storage. In 05 I didn't know about parasitic draw with the opti. The second year I had promises made to top off charge during winter... Didn't happen and charging battery went bad. Pulled batteries for a couple of years but these 70 lb pm1's were a chore. Installed cutoff switch and still had reasonable charge with one top off during storage. That set of batteries installed in 08 lasted 7 years until I sold the boat. I was fishing to's until that point. I was using a Lester charger specifically designed for AGM.

Savage:

To quote Forrest Gump, you just can't fix stupid. :) I was asked a question about transducer placement a year ago, at the boat ramp. Guy said he could not get any depth readings above maybe 20mph. Said he had been playing with it for several years with no luck. I walked around back to look and it looked like he had been in a 22 rifle war. Never saw so many holes on a transom. Never saw so many holes with NO sealer or anything to plug 'em. Never saw a transom so soft. You could push down on the bottom of the gear case and black liquid would come out of several of those holes. Told him I would not put it in the water again until it was looked at (it was a 'glass boat with a 150 on it) - he might have the motor joining him in the cockpit if he was not careful, and at the very least might leave it on the bottom of the river.

My circumstances are hugely different from the OP here. My boat is stored in my basement. Chargers are built in and are always plugged in unless I am out with the boat. Boat is out typically once per week this time of year unless we get a long freezing snap, and is out 2-3 days a week during the summer. So even if I had a 1 amp / hour parasitic drain, I would not notice. If I were storing remotely with no local power handy, I would likely opt to take the batteries with me and keep them charged at home. Yes they are heavy. I am running 24v TM so hauling 3 batteries would be a hassle.

I would hesitate to leave any battery alone and disconnected for 3 months. I ruined my John Deere tractor battery after only two years, as it doesn't typically get used for 3 - 4 months and has a master off with zero parasitic drain. When I would go to crank it for the first mowing pass each spring, it would barely crank. At the beginning of the third spring it would not only not crank, but it would not charge either. Replaced battery and have kept it on a automatic trickle charger for 6 years now and the second battery is still working well. Note it is trickle-charged only during the winter since it is run about every 5 days once we see grass growing.

I would think that if the OP doesn't like transporting some lead, that a master cutoff might be his best alternative. For me, it would simply represent yet another mechanical point of failure. I have been working with computers for almost 50 years now, and I hate any sort of contacts. Cable connections that are not soldered. Edge connectors for circuit boards. Switches. 90% of the problems I have had to solve were related to those. The electronic parts themselves are pretty reliable. As a result, I am not one to add another penitential point of failure if there is any other option that is not too egregious.

I realize you deal with all types of people, boats and such. The aluminum hull issue won't bite me as I won't ever own one, I am a 'glass person (Bass Cat). I don't remote store although if my wife and I end up on a lake/river, I will certainly build a boat house with a lift to store the thing, and there will definitely be power available to keep the batteries hot. Had a family member that bought a bass boat back in the 70's and stored it remotely. He was replacing both batteries (back then it was a 12v cranking battery and a 12v TM battery) every two years. Wasn't able to fish a lot so it sat idle for several months at a time, and even with batteries unhooked (a requirement of the storage place he used) it ate batteries regularly.

Quote:

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Originally Posted by OldTimer57

Seems that the usual group 31 battery claims a 125 ah capacity. That is it can provide 125 amps for one hour, or one amp for 125 hours.

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Not true. You might want to read this to gain more more insight on ah rates and how they're actually determined. You will learn about Peukert's Affect which explains why it's not "simple math".

Also, all of the recommended gp31batteries in this link for an Optimax are between 100 - 105ah (20hr rate) as stated by battery manufacturer with the exception of D31 Optima which is 75ah. The 20ah rate is determined with a continuous 5amp load - industry standard set by BCI.

The 20ah rating definition of usable voltage, 10.5v (which may be fine for trolling motors and most electronic devices), won't work for starting an Optimax. My dealer (like many) installed a battery that only just met Optimax minimum requirement of 800CCA, and before upgrading to the PM-1, I learned the hard way I needed to constantly monitor battery voltage to ensure my Optimax would start. My anxiety level definitely went up when battery voltage dropped below 12v!

I'm not sure how one can determine actual state of charge on an AGM battery without a load test. Used to be done by checking specific gravity of each individual cell, but that's not possible with sealed batteries (AGM, gel, or VR sealed wet cells). Suffice to say if parasitic draw exists, and is significant enough, it will indeed cause a discharged battery and in short order too.

I agree with Savage and others who feel a battery switch is right for their application as long as the battery switch is designed to provide the max current capacity of the battery in use during starting operations. As a result of all the recent discussion on this topic, and my newly acquired knowledge of the ABYC recommendation a battery switch be installed if battery capacity exceeds 800CCA, I will be installing one on my boat in the very near future. :wink:

Note I was not talking about any particular discharge rate. A 125ah battery can supply 125 amps for one hour, or 1 amp for 125 hours or anything in between. At that point it will be pretty useless for running anything. This is different from the numbers you are quoting above. This number is pure capacity. I buy batteries measured like this all the time for my radio-controlled stuff. A common battery pack for a R/C receiver and servos is 500mah, it will provide 500 milliamps for one hour or one milliamp for 500 hours. After either of the above, it will be below 3.6 volts or so and not be usable until recharged.

BTW my background is electronics, so I am familiar with Peukert's, but that is on the OTHER end of the extreme from what we are talking about. We are talking about very small parasitic current drains, not 100 amp near-short or heavy duty starter motor levels. I'd bet my estimates for current drain given his stated 70% in N hours measurement were pretty close.

My comment was, and still is, simply this: "if a master cutoff is useful for your circumstances, then it is likely a good idea. But it is most definitely an additional potential point of failure as well. Since it offers me nothing at all, except the possibility of a failure, I don't use one.

Lots of good info, lots of opinions (which we are each entitled to).

Bob- I'm glad the switch solved your problem. Won't hear any argument from me on "success". :wink: