Battery maintaince

[RDW]

I do not want to show all my ignorance but here goes. You are wanting to keep the specific gravity up. You top off the batteries with distilled water. I have Rolls T 250 batteries (4 house)which are about 4 years old. I have tried to keep them topped off and equalized 2-3 times a year. I am not on my boat much. I am planning on doing the World ARC in 2017.
Is it ever good to top off with battery acid instead of distilled water?
What should I do to check my batteries to make sure they are in good enough shape for the World ARC?
RDW

[a64pilot]

Never add acid to a battery, only distilled water.
To determine health only way I know how is to do a capacity check

I'd replace them for something like the World ARC, they will be six yrs old then, probably be good, but who knows for sure? Cap check should tell, but still?

[RDW]

Originally Posted by a64pilot

Never add acid to a battery, only distilled water.
To determine health only way I know how is to do a capacity check

I'd replace them for something like the World ARC, they will be six yrs old then, probably be good, but who knows for sure? Cap check should tell, but still?

Interesting, so do a battery capacity check but replace $2,000 batteries just because they are 6 years old. The ones I replaced were 15 years old!!
How do I do a capacity check? Or point me to a reference.
RDW

[a64pilot]

Do a Google search and do some reading, this is a good place to start
BU-904: How to Measure Capacity – Battery University

Myself if I were to set out on the ARC, I'd probably put new batteries in, but that's my opinion. You got 15 yrs out of the last set, but were they being used / cycled 7 days a week, for fifteen months?

[rwidman]

You don't add acid (unless it was spilled) because only the water evaporates. The acid stays in the battery but becomes too concentrated as the water evaporates.

[RDW]

After doing a little reading, I think I would need a fairly expensive instrument that would give me a good estimate. I will continue to read. Thanks for the help.
rdw

[skipmac]

Originally Posted by RDW

After doing a little reading, I think I would need a fairly expensive instrument that would give me a good estimate. I will continue to read. Thanks for the help.
rdw

I did a quick read of that article which seemed to reject the accuracy of a simple discharge test. Perhaps for some lab purposes I guess but for getting a very good idea of the capacity of a bank of deep cycle batteries on a boat it is far more than adequate and no expensive or special equipment needed.

Have done this numerous times on mission critical batteries. Might be accurate within decimal points but will absolutely confirm if your batteries are relatively healthy or on their last legs.

[a64pilot]

Originally Posted by RDW

After doing a little reading, I think I would need a fairly expensive instrument that would give me a good estimate. I will continue to read. Thanks for the help.
rdw

Actually I think that's a pretty accurate assessment,
I do cap checks on aircraft batteries, they are required on an annual basis by what is called the instructions for continued airworthiness, although they are almost never done. I use a 600W aircraft landing light as a load bank, and truth be known it's not really that accurate a method, reasoning is of course amps drawn is variable with battery voltage, so the discharge rate is slightly variable.
But the intent is to identify a battery that although will crank an engine, doesn't have the reserve capacity to continue to operate the avionics in the event of a charging system malfunction, the landing light is good enough to spot batteries that no longer have the reserve capacity as newish batteries pass the test with a wide margin, so when you get close, it's time for a new battery.
So without expensive, lab quality equipment, it's tough to determine exactly the capacity of a lead-acid battery, largely because it will vary for seemingly unknown reason by a significant margin from one day to the next.
And it seems at least some batteries seem to die rather quickly as opposed to a slow gradual decline, although it may be simply that you think a battery is fine until it degrades to the point to where you notice, if you only use 20% of your banks capacity, then you think your bank is fine until it degrades by 81%. I suspect this is the biggest reason some seem to get really long lives out of their banks.
All this leads me to think that if your going on something really important , like a Circumnavigation, I think it's prudent to not start out with 6 yr old batteries, assuming of course that your boat is the type that has a lot of electric equipment, and or it makes life easier and you have come to become a little dependent on it. I know I have.

[S/V Illusion]

Originally Posted by RDW

Interesting, so do a battery capacity check but replace $2,000 batteries just because they are 6 years old. The ones I replaced were 15 years old!!
How do I do a capacity check? Or point me to a reference.
RDW

Value judgments are quite subjective. That you paid $2000 for batteries has little to do with it. Rather, capacity, charging regime and number of 'duty cycles' determines the useful life you can expect. You can kill expensive. Batteries as easily as cheaper ones.

[btrayfors]

Rolls batteries are about the best flooded lead-acid batteries out there. Many users get 10-15 years out of them.

Sounds like the OP has been taking decent care of his 4-year old Rolls batteries. Keeping the electrolyte level well above the plates, charging regularly, and equalizing periodically should help extend battery life.

It is correct to say, however, that there are only two ways to reliably check the capacity of these batteries:

1. a controlled 20-hour discharge, carefully monitored; and

2. measurement with a sophisticated (and expensive) inductance-capacitance instrument, like the Midtronics series.

The first is by far the most accurate, is inexpensive, but takes quite a bit of time.

The second is quick and can be reasonably accurate if used by someone who knows the instrument and has lots of experience measuring battery capacity.

Although I have LOTS of experience with both methods, if I were planning to do a world-girdling ARC I'd check my battery capacity using both measurement techniques.

Provided the measurements indicate remaining capacity of at least 95% of rated capacity, I'd go with the installed Rolls batteries.

If, however, battery capacity were much less than that, I'd probably go with new batteries since, in my experience, when capacity falls much below 90% the battery may one day soon quickly fall below 80% and need replacement.

Bill

[RDW]

1. a controlled 20-hour discharge, carefully monitored; and

Should this be done on individual batteries or on the group?
At one point what I was reading something that said to do it a zero degrees centigrade. How?
Is anything different as far as doing the test for these which are house batteries versus starting batteries?
RDW

[skipmac]

Originally Posted by RDW

1. a controlled 20-hour discharge, carefully monitored; and

Should this be done on individual batteries or on the group?
At one point what I was reading something that said to do it a zero degrees centigrade. How?
Is anything different as far as doing the test for these which are house batteries versus starting batteries?
RDW

I think trying to do the test at 0 C is going way beyond what is necessary and what you would be trying to accomplish here. At least for me, a battery capacity test is to get a reasonably accurate determination of the batteries remaining capacity and use that information to help decided if it's time to replace. I would of course also be factor in future cruising plans IE how soon, how far and where I'm going.

Regarding separating the batteries for testing. Of course that would not be a bad thing, other than the extra hassle and testing time. Again, for me, I would do a test of the whole bank as wired in the boat and if the results looked questionable, then consider testing separately.

[btrayfors]

Right: individual battery testing is better, but testing the whole bank would give you a good idea overall.

You do NOT need to do the test at 0 degrees Centigrade. Where did that come from?

Do the test at room temperature. Deep cycle batteries are rated for a 20-hour discharge. Thus, a 100AH battery should be tested with a 100/20 amp load, i.e., a 5A load.

Unless you have some sophisticated stuff available with which to put a constant load on the batteries, just do the best you can to approximate the 20-hour load. For example, if you start out with a 5A resistive load consisting of lightbulbs, their resistance will change over the 20-hour test period....they won't stay at exactly 5A as the voltage drops. Nevertheless, this is a fairly good way to test.

Ideally, if your batteries have 100% of their capacity remaining (this is NOT the same as being 100% charged), and you apply a C/20 load to them, they should last ~ 20 hours before reaching the final voltage of 10.5VDC.

If they last only 19 hours or so, you're golden. If they only last 15 hours before reaching 10.5VDC (under load), then they've lost a lot of capacity and need to be replaced.

Before testing, be absolutely sure that your batteries are 100% charged at the recommended voltage. I'd use 14.8VDC for those Rolls batteries...overnite or longer.

Bill

[sailorboy1]

Wouldn't seem to me to matter what the % of rated capacity remaining the batteries have as long as it meets your needs and you know the number. Other than an indication of battery life remaining it doesn't really matter much to me if my batteries are at 95% or 90% capacity as it doesn't really make much difference in real use.