Batteries keep dying

[swimmin' for shore]

I have a dual battery system on my 16' aluminum boat. The batteries don't seem to be holding a charge, and for that matter, even seem to be draining whatever charge I put into them. When I put the speed charger on either of the 2 batteries, they register below 20% of full charge. No matter how long I leave the charger on, they won't go above 70%, either. Last Wednesday, I charged the batteries to their 70% threshhold, took the boat out for a run, shut it down to fish for about 6 hours, and came home. While fishing, the only thing I ran was the anchor light and the radio for a short while. At the end of the night, I started my motor and took it in. When I got home from the river, I shut the battery switch off and left it so. Over the weekend, I took a 5 hour drive with the boat to help my dad put his own boat in the water. We never finished his work, and didn't make it to the water. I drove home on Sunday, hooked up the charger to check battery %, and it registered between 7-10% charge on each battery.
For history on this, these are Wal-mart deep cycle batteries. The other set were, as well. I am running a Johnson 50 hp motor currently, but I lost the last set while running on a Mercury 40 hp motor. By that, I believe that this issue does not have anything to do with the motor. Both motors have charging systems that are working, although the Johnson is putting out slightly less than I believe it should be, at only about 13.0 V.
Setup wise, each battery has one hot lead leading to the perko isolator. Beyond that, there is nothing else hooked up on the positive side. On the negative side, pretty much everything on the boat is grounded. I probably need to run a bus bar, but haven't gotten that far yet. I'm very good about remembering to turn the switch to the off position. I've checked it and am confident that I have no draw from any wire when the switch is in the off position. My batteries both sit on rubber-backed carpet, which sits in a wooden-based enclosure.
Sorry for the long post. Thanks in advance for any help you can provide. SFS

 

[Fl_Richard]

Re: Batteries keep dying

Something may have been dragging your batteries down but if you cant charge them past 70% their now toast!

Sounds like a shorted cell to me.

 

[SS MAYFLOAT]

Re: Batteries keep dying

Deep cycle batteries do not like a fast charge or a high amperage rate of charge. It cooks the plates and shortens the life of the batteries. Been there and done that myself. After learning to use a trickle charger for a few days, my deep cycle batteries are lasting a whole lot longer.

 

[Silvertip]

Re: Batteries keep dying

Have the batteries load tested at any auto store (usually free). Be prepared to purchase some new batteries. If they don't hold a charge and you are absolutely certain there is no drain, then the only answer is the batteries are bad and not capable of "holding" a charge.

 

[Nandy]

Re: Batteries keep dying

Deep cycle batteries do not like a fast charge or a high amperage rate of charge. It cooks the plates and shortens the life of the batteries. Been there and done that myself. After learning to use a trickle charger for a few days, my deep cycle batteries are lasting a whole lot longer.

I echo Mayfloat advise. Get you a good marine charger, 2 bank for cranking and deep cycle. You did not specify but are you using a deep cycle for your motor? That is going to cause you problem too. You need a cranking battery and a deep cycle battery. Those yellow batteries at walmart have not let me down yet.

 

[swimmin' for shore]

Re: Batteries keep dying

I am planning to take them to a place that deals with batteries and electronics down the road here. I admit that I generally speed charge them when need be, but I'm a little confused as to why they're dying in the first place. I very rarely troll. I have a trolling motor, but it's really just the emergency plan. The only emergency it won't cover, of course, is dead batteries. Listening to a radio at night and running an anchor light is not killing 2 deep cycle batteries. Also, I agree that I probably have a dead cell, but this isn't a dead cell on one 6-month old battery. It's a dead cell on 2. And last year's batteries weren't but a little over a year old, either. It's getting to be a kinda expensive problem.
If I replace these, I will go ahead and get a cranking battery and a new deep cycle. Thanks for that advice.

 

[Silvertip]

Re: Batteries keep dying

Don't be concerned about a deep cycle battery as a starting battery. Not recommended but not impending doom either. They work just fine in that capacity. Look -- if a battery is totally disconnected from all circuits as you say they are, then there cannot be any current draw so that leaves bad batteries. Unless you actually check for current draw, you won't know. An electronics store doesn't load test batteries. An auto store does. And yes, two batteries, new or not, can be bad in six months. From what? A poor charger. Not charging immediately after being deeply discharged. Excessive gassing during charging. Low on electrolyte (distilled water), too high a charging voltage on the boat to name just a few.

 

[swimmin' for shore]

Re: Batteries keep dying

I must have misstated. I'm taking them to a place that deals with battery issues. It is an auto store. I'm certain-positive-that there's no draw when the batteries are off, and I'll accept that they're bad batteries. My problem is that this is the 2nd set of batteries in less than a year that are dead. That goes through 2 seperate motors, as well so I at least like to think that it's not a problem with the charging system. Very confusing. I do check regularly for full water. The charger is a speed charger from Wal-Mart. They're pretty cheap, so that could be the problem. As I said, I do tend to speed charge at the higher amperage, so that could be the problem. I don't have such a problem with buying another set of batteries, but I hate doing it if I can't solve the core issue first. Anything I should check before I go buy new batteries?

 

[flargin]

Re: Batteries keep dying

It sounds like you don't charge when you get home, but fast charge before you go out. This would be a great way to kill your batteries.

DOA batteries can happen, but are not that common, I would check:

1. charging system working on your motor? check the voltage of the charger. if it is too high/too low you can kill your batteries.

2. house charger cooking your batterys? your fast charge could be boiling off the water/acid. Do you ever have to add water? how much? do you use distilled water?

I would say you should get out of the habit of fast charging, and get into slow charging & maintaining your batteries.

 

[Daley]

Re: Batteries keep dying

A couple posts above have said it and I'll reiterate it - fast-charging WILL kill any battery, no matter what. Yes it's convenient cuz you generally don't know about a dead battery until you *need* it so that's WHY people use fast-chargers, but the fact is they kill batteries.

 

[Silvertip]

Re: Batteries keep dying

Actually fast charging is a relative term -- as in what rate. Battery manufacturers use a percentage of battery capacity as the charge rate so for most batteries a 10 - 15 amp charge rate is very acceptable. Smart chargers are the preferred charger as well. A trickle charge is not recommended for charging but is recommended for maintenance during storage or short term layup.

 

[bustermin]

Re: Batteries keep dying

just curious, you said you disconnected the batteries via a switch. have you verified that the switch is actually disconnecting, did you check voltage on both side of the switch before and after you hit the switch? i have had a switch go bad and not shut off the voltage and drained the battery. this of course will not cure the "Bad Battery" issue but might explain the batteries going dead while not in use.

 

[mike64]

Re: Batteries keep dying

Not to hijack, but I think this question is relevant to the advice people are giving swimmin'. If you use a smart charger is it ok to start at 10 amps? I charged my battery that way all last season and the smart charger would start at 8 or 9 amps and gradually drop down to 2-3 amps before it said "full". This didn't seem to hurt the battery any. I start at 6 amps now to be on the safe side.

 

[Daley]

Re: Batteries keep dying

Silvertip has it right - it's all relative. You wouldn't pump 10 amps into a set of 8 AA batteries (which equals 12V), but doing that to a car/boat battery is a good way to prolong its life.

Being the cheap SOB that I am, I don't own a "battery charger" per se - I use the power-supply from my electronics workbench because the output is WAAAY more 'filtered' and I can regulate the current as well as the voltage. For my bikes, I start out with 2-3 amps at just over 12.5V and because of the current-limiting built into it, I run no fear of cooking a battery. For the boat/car/truck, I start a little higher, obviously. When the battery is fully charged, it's not drawing the current like it did when I hooked it up, so it eventually tapers off to zero.

That being said, a smart charger is just that - SMART. Getting one would be a SMART thing to do.

 

[Silvertip]

Re: Batteries keep dying

The tapering effect of a good charger is normal operation regardless what charging current you select. As I remember, battery manufacturers use 20% of the battery capacity as the recommended charge rate. A 50 AH battery would then be charged safely at a 10A rate. A good smart charger can be plugged in and left on continuously as mine are. I tend to do things a little differently however. I have a low current on-board maintainer for the start battery as it is rarely deeply discharged. It gets plugged in at the dock and when in the garage. My troller battery has a bigger charger that is also plugged in continuously at the dock or when in the garage. In my view there is no need to spend a great deal of money on a dual or triple output smart charger when one of those outputs is dedicted to the start battery. Different story if all accessories are powered from the single starting battery.

 

[j_martin]

Re: Batteries keep dying

When a battery is discharged, small crystals of lead sulphate form on the plates. If it is left in a discharged condition, the crystals may either grow, or actually fall off the plates, losing the sulpher to the sludge pile in the bottom of the battery. That's called a sulphated battery.

All lead acid batteries will eventually sulfate no mater what you do, but leaving them in a discharged state, and especially transporting them in a discharged state accelerates the process.

There are pulse mode chargers that can recover sulfate that is still on the plates. Some of the real high buck chargers have them built in. Inexpensive battery "de-sulphaters" can be made. Lotsa info on the web.

Another thing about automotive and marine batteries is that they will self discharge in a relatively short period of time (month or so) unless maintained. Batteries discharge by an electrolyc process, and because of the metals (antimony mostly) that are added to the lead plates to make them mechanically strong enough, a local electrolysys takes place, even if there is no load. That is normal.

If a battery will be stationary and not subject to vibration, other alloys can be used that make the plates strong, but brittle. That's why the batteries at the telephone company last 10 years. In a boat they would last days or weeks.

If you are in the habit of discharging the batteries, then transporting them over rough roads, then leaving them discharged untill the next use and quickly charging them up, then you are in the habit of buying a lot of batteries.

hope it helps
John