Difficulties in testing batteries

[Poozer]

I have 1,000 AH of Toyama hybrid gel batteries in my house bank (5 x 200AH), but during a night passage, I'm only getting about 10 hours of discharge before I hit 10.5 volts and the alarms start going off causing me to run the genset. This typically happens about 4am on a night passage.

This unhappy state has brought to light several issues:

1. Assuming I have 50% of available capacity, then in order to use 50% of the capacity of the bank in 10 hours I would be drawing an average of 50 amps. The ammeter built into the Matervolt charger is nowhere close to this, so either a) the ammeter is incorrect and I'm drawing 5 times more than I think I am. Or b) My battery bank is toast.

2. These batteries were (supposedly) installed new in 2009, so they should still be operating per design.

3. I am installing a new ammeter to verify, and assuming my true amperage readings are less than 50A (average), I must have degraded capacity in the house bank. So I will need to test each battery to see if it needs to be replaced. This raises the issue of how to best verify the state of the batteries.

I have scoured the Internet and can't find any charge, vs. voltage data for my Toyama hybrid Gel batteries (certainly won't be buying them again), so I'm going to have to improvise.

I figure if I test each battery in turn by connecting it to a DC battery monitor that is connected to a 20amp load, which is controlled by a voltage switch that will shut the load off when the voltage drops below 10.8 volts, I can then read the Amp Hours consumed during the test.

This raises some questions, that I am hoping you can help me answer:

1. Is this a valid approach for testing deep cycle batteries?
2. What % of rated AH capacity is acceptable for the test?
3. What is the result threshold for replacing the battery(ies)

This is making my head hurt, so I'm hoping someone who has dealt with this before can help!

[noelex 77]

I think your batteries are toast.

The way you are suggesting testing them is the best way. It does not do the battery much good so its not a test to do often, but in your case this is exactly what I would do. It may be only 1 battery that is defective
Make sure they are fully charged first. Your charging system may be at fault so charge them an alternative way if possible.
The normal cut is slightly lower than 10.8v, but that wont make much difference.
A new battery should test about 90% of its rated capacity.
Most people discard them when they only test about 70% , but it depends on your requirements one of my batteries was down to 60% 2 years ago. I have a second, newer, battery bank so I have kept the old battery abusing it somewhat ( often down to 20% or so) and its still measuring the same 2 years later. My newer batteries have rarely needed to be used at all. I know the older battery probably will fail soon and possibly suddenly, if you only have one house battery bank this strategy would be risky.

Given the short life you have experienced make sure you check the charging voltages and discharge habits (even deep cycle batteries will not survive many cycles if you are taking them down the 10.8v)

[Poozer]

Originally Posted by noelex 77

I think your batteries are toast.
A new battery should test about 90% of its rated capacity.
Most people discard them when they only test about 70%

Hi Noelex,

Can I ask a clarification question? Do you mean that a new battery would deliver 90% of it's rated capacity before the voltage drops to 10.8v? So in the case of a 200Ah I would measure 180Ah before the battery voltage drops below 10.8V?

Thanks for your advice on the charger. I'll definitely check that as well.

Regards,
Doug

[noelex 77]

Battery specs vary a bit, but most quote the end voltage a bit lower than 10.8v, but the voltage starts dropping rapidly at these low values so the cut of voltage will not make much difference.
The discharge rate is important you are using C10 (10 % of the capacity), but some batteries specify their capacities at lower discharge values.
Temperature also plays some role

The bottom line is that stopping at 10.8v if I got 180AHr out of a 200Ahr battery I would consider that new or close to new performance.

I think you find all (or hopefully just some) of your batteries will have much lower performance than this. Your OP suggests you will only measure about 1/5 capacity (40AHr) so I do not think you will have difficulty interpreting the results.

[twistedtree]

My first guess would be that you have a bad cell in one of the batteries. There are 5 12V batteries wired in parallel? One bad cell in one battery will make the whole lot appear bad, and if not corrected will trash the remaining batteries.

Here's a very simple test you might try:

1) Charge up the bank in its current configuration.

2) Isolate each battery and measure it's open circuit (no load) voltage. Chances are pretty good that the offending battery will identify itself with a lower voltage that all the others by 1+ volts. Note that you might need to disconnect all the batteries so they are all isolated from each other, and let them rest for an hr or so after charging the voltages settle down.

3) Assuming you find the bad battery, wire up the remaining batteries and put them back in service. You should find they work well and can be used until you can replace the bad one.

There will be lots of debate over the virtues of replacing one battery in a 2 year old bank as opposed to replacing them all. With a 5 battery bank, you only need to get 20% more life out of the remaining batteries for the replacement of a single to be cost effective, so I'd replace just one, assuming you can find a replacement.

[DeepFrz]

Bill lays out what is required in this current thread

http://www.cruisersforum.com/forums/...tic-62687.html

You shouldn't be regularly discharging your batteries to 10.5 volts. This will significantly shorten their lifespan.

[djmarchand]

I agree that the batteries are probably toast. Why? Because they are not deep cycle batteries. IMHO no flooded cell or gel cell batteries are "hybrid". That is just marketing BS. AGMs can be hybrid as there really isn't much difference between an AGM made as a starting battery or as a deep cycle battery.

Other than AGMs there is only one way to be absolutely sure that you are buying a deep cycle battery. That is to buy 6V golf cart batteries and wire them in series/parallel to get the voltage and amphour capacity that you need. Costco has them for about $75 each which is the cheapest real amphour storage that you will find.

BTW the spec for most deep cycle batteries is amphour capacity measured at an amperage draw of 1/20 of their capacity. So for your 1000 amphour bank that would mean testing them at 50 amps draw. Testing at 20 amps should increase the capacity significantly. But obviously you are getting no where near that capacity.

[Poozer]

I'm almost finished building my load tester, but in the meantime I have been checking all the charging systems on the boat.

1. 110v charger connected to genset is ok
2. 240v charger connected to shore power is ok
3. Solar panel regulator is OK
4. Port engine alternator 0v (need to look into that. PO said it never worked)
5. Stbd engine alternator suspect. It's putting out 14.6v

Is 14.6v too high, or is it within spec? My research turned up a recommended voltage for alternator voltage regulator of 14.4v. Will 0.2v more reduce battery life?

Thanks for all your helpful comments so far.

Doug

[noelex 77]

Its better to use the changing voltages specified by the battery manufacturer as they do vary a bit even for the same battery chemistry.
If you cannot find this information 14.6 is generally too high for gel batteries (particularly if it maintains this voltage I instead of rapidly dropping down to a lower absorption then float voltage), and can shorten the life, but its important to remember to measure this at the battery end, not at the alternator. Its not clear from your post where the voltage was measured.

.

[Poozer]

Originally Posted by noelex 77

?..but its important to remember to measure this at the battery end, not at the alternator. Its not clear from your post where the voltage was measured.

Sorry, I should have specified. All my measurements were at the battery terminals.