deep-cycle battery left on charger?

[audiolofft]

Hi all,

When I leave my boat for up to 2 weeks at a time, is it better to leave the deep-cycle batteriy on the built-in Catalina 27 shore-power charger, or make sure the batteries are charged and switch off the AC shore power. I could also leave them on a small solar panel trickle charger (about 1 amp). Some of my sailing friends leave their boats off the shore power when they go away, or on a small solar panel. The reason I ask is that my marina installed a new deep-cycle battery two years ago, and this spring I was told it wouldn't hold a charge. (the marina keeps the batteries on a charger over the winter indoors). I expected longer service than 2 years from a new deep-cycle battery. The other battery is a cheap Canadian Tire Nautilus 12-volt marine battery, and it's on its 5th year of service!
Typically, I leave the boat on the shore-power charger when I go to the city but perhaps it's overcharging the deep-cycle battery, hence shortening its life.

--Alan

 

[Don S/V ILLusion]

What kind of charger and what is the voltage under maintenance cycle (if it has one) at the terminals? Without knowing this info, it's a wild guess

 

[jrowan]

What usually kills deep cycle batteries is not overcharging, but overdrawing them when in use when on the hook. Overnighters when you're running interior lights, mast lights, steaming, VHF, stereo etc. Especially using an inverter, or a 12 volt fridge - sure fire battery killer. If you draw down your batteries repeatedly to below 40 % of their capacity or to the point where there reading under 12 volts, they will sometimes not recover because you can damage the lead plate chemistry permanently. I try to be very conservative & sparing with battery usage, turning on only what's necessary. One bank is for house, one for engine starting. But beware that one bad battery will draw the power from the good battery as they always want to equalize their current output.

 

[Jon_E]

Did the acid level ever drop to expose the plates? That is very damaging to batteries. It is my understanding that once the plates are exposed, that part of the battery is permanently gone and will never be usable. "JRowan" is correct that you should not draw your battery much below 40%. Although a deep cycle battery can be drawn down to as low as 20% (hence the name, "deep cycle") there is a correlation between how low the battery is drawn down and the battery life (battery life = number of discharges and recharges). If you draw the battery down too low, some individual cells may reverse polarity (in other words, ruined battery).

It is also possible you have a bad battery from the factory.

When replacing batteries in a bank, it is better to replace both (all) of them at the same time with the same type, even if one battery is still good. Otherwise, the stronger battery will constantly try to charge the weaker battery.

To answer your question, my shore power is "on" all the time. The battery charge is never drawn down too low, the fluid levels are checked twice a year, and the terminals are kept clean. They are two deep cycle marine batteries from CostCo wired in parallel that are still going strong on their fifth year after purchase.

 

[audiolofft]

Thanks to Don, Jrowan, and JonE for your help. Don, the built-in charger is a Charles Marine Ferroresonant 3000 series unit. Its DC output is 15 amps at 12 volts and it has a built-in DC ammeter, which at the moment indicates either 0 or 1 amp, as best I can read it hanging upside down halfway into the battery compartment. If the DC ammeter is reading properly, then I would assume it's on a trickle charge maintenance mode, since both my batteries are fully charged.

Jrowan, l tend to be conservative on overnights (no fridge); if I run the anchor light overnight and one or two cabin lights until bedtime plus the stereo, the batteries are at about 80% to 90% charge in the morning (on my most recent overnight, for instance).
I tend to be vigilant about fluid levels and as far as I know the the plates were not exposed on the two batteries during the summer season. Of course, I hope they're maintained proplerly over the winter--the marina keeps them indoors on chargers--but there's always the possibility of neglect during Northern Ontario's long 6-month winters, although I've been pleased with the maintenance on my boat's diesel and various systems.

--Alan

 

[audiolofft]

What kind of charger and what is the voltage under maintenance cycle (if it has one) at the terminals? Without knowing this info, it's a wild guess

Don, see above for info on the built-in charger. I'm running an experiment--I switched off the AC charger. The voltage at the battery terminals (batteries are in parallel) is 12.8 volts. I washed the dishes, using the on-demand Shur-Flo pressure system and ran the Mobicool 12-volt cooler while doing so (the cooler pulls about 5 amps); the % charge after doing that went down to 75 to 80%; voltage at the terminals sank to 12.66 volts. I'm leaving the cooler running for awhile to pull the batteries down somewhat so I can see if the DC charger ammeter works when I switch the AC shore power back on.
One further note; I used a hygrometer (hydrometer?) to check the electrolyte in all the cells. They read excellent and are very close to each other. Of course I don't know about the 2-year old deep cycle one that failed, except that I maintained it as I did the starting battery, a now 5-year old "Nautilus" from a tire chain in Canada (Canadian Tire). I run the system at all times set to "Both" on the big Perko battery switch.
Will report on the ammeter readings later on when I switch on the shore-power DC charger. --

 

[audiolofft]

Ok, I switched the shore-power and built-in charger back on. Before I did that, my % charge meter on both batteries read 90%, and the voltage at the terminals was 12.74 volts. When the charger was switched back on, it appears the DC ammeter is working because it read about 3 amps of current, which seems about right since the batteries were at 90% charge.
I just checked it again, and the ammeter is back to 0 or 1 amp, and the voltage at the terminals is 13.28 volts.
From all this, I've concluded that the built-in AC charger is working correctly and keeps the batteries at 100% or Full, as my charge meter indicates. The voltage at the terminals is 13.28 volts, which in my judgment, isn't too high, and the DC ammeter is at 0 or 1 amps.
I figure the 2-year old deep cycle battery that went kaput was either defective, or wasn't maintained properly over the winter.
At one point two years ago, I had a fairly large solar panel connected early in the season without a voltage regulator. After a month or so, I bought one and installed it, so there is a possibility I overcharged running the solar panel without a voltage regulator on it (I no longer use it; it was unwieldy; if I go on a long cruise, I'll install it again). But that should have damaged both batteries and it didn't. The cheapo Nautilus starting battery is in its fifth year and all the cells are healthy.
Thanks for all your help and tips.
If you disagree with my analysis, please share your thoughts.
--Alan

 

[Stu Jackson]

You old charger is just that: old.

You might want to consider upgrading your charger to the new technology. We've found that a small investment in a new charger has an immediate ROI, since it keeps your batteries healthier.

Try this: http://forums.catalina.sailboatowne...p=880275&highlight=installing battery charger

 

[jrowan]

I use a Zantrax hardwired charger wired throught the 110 volt panel which works well automatically. I also use cheaper priced standard lead acid deep cells bought from Sams Club. I don't believe in paying more for a big brand name, (but I believe their's are made by Duracell). I think its more important to buy a dep cell with as many Amp hours of capacity that you can reasonably afford. Capacity is more important then anything else. The larger the capacity, the less the percentage of the power output you will draw down. Hence I believe that bigger batteries tend to last longer. I would be careful with non voltage regulated solar panels. They can boil a battery which stays dormant for long periods of idle. I also don't like mega alternators like Balmarls. They are overkill, & most batteries cannot accept the huge charge rate they produce. Lastly, you mentioned cold Ontario winters. That may also be a culprit. Exceptioanlly cold temps can actually freeze the electrolyte inside the battery if it gets below zero celcius for a long period of time.