House Battery Condition

[Nodak7]

I have six (6) Trojan T105 6v Batteries for my house battery system. They have been in service for over 8 years now which is well beyond my expectations. I am a bit nervous regarding their age. The voltage shows good and the Specific Gravity is still good. The only point that concerns me is it seems the bank is running down faster overnight. Is there any other test I can do to determine condition? Or should I just bite the bullet and replace the bank since I got well over the normal bank life expectancy with them? Your thoughts?

 

[Davidasailor26]

At 8 years they don’t owe you much, and loss of some capacity is consistent with the symptoms you’re seeing. Specific gravity and resting voltage could still look ok while actual capacity decreases from sulfation on the plates. The best way to test them is a controlled 20 hour discharge test. General steps for that are:
- Fully charge the bank.
- Separate the parallel batteries into just series pairs for testing
- Divide their theoretical 20 hour capacity by 20
- Apply a load equal to that amount (it should be 11.25 amps for two T105’s in series)
- Measure the time it takes to hit 10.5V.
- Multiply the number of hours it takes to get to 10.5 by the constant current drawn to find the actual capacity of the bank. For example if it takes 18 hours that pair is 202 amp hours, or about 90% state of health.
- Recharge to 100% SOC as soon as possible.

You might find all three pairs are about the same and generally depleted, or you might find you’ve got one battery worse than the rest. Admittedly with three pairs of batteries this will be a little bit of a time consuming process, especially if you don’t have the equipment to do it already. I use a spare shunt for measuring current, and a cheap inverter and incandescent light for the load.

 

[Ralph Johnstone]

The only point that concerns me is it seems the bank is running down faster overnight.

Does this upset your operation in any way ? If not, keep using them until the slowly diminishing capacity does cause a problem. Get the most use out of them you can before renewing them.

 

[dlochner]

The 20 hour test @Davidasailor26 describes is the standard and most reliable method.

There are 2 factors to consider, state of charge and capacity. What you are measuring with voltage and specific gravity is state of charge which is important in the short term. At 8 years old what you should be concerned with is capacity. New, the Trojans probably have about 220 ah of capacity each, for total of about 660 ah at 12v. By now that capacity is much lower than 220 ah each which is why they are very deleted after a night on anchor.

Time to consider new batteries, these owe you nothing. Eight years of 12 month use in Florida heat is tough on a battery.

 

[Benny17441]

All the batteries in one bank do not degrade at the same rate. I run a 36V Golf Cart with six 6V batteries and whenever it feels a sluggish I conduct an individual load test on each of the batteries and I usually find one battery in the group that is bad. The procedure is to fully charge them all and then disconnect them. Since you are running 12V you can remove the wires to the negative poles of each battery. A cheap load tester will do and one can be purchased at Walmarts or Harbor Freight. Connect the (+) and (-) to one of the batteries and it will give the actual voltage and show in a color scale whether OK, Weak, or Bad. The tester will have a toggle switch that when activated it will introduce a resistance or load to the current and the meter will show a drop in the voltage. If the needle show OK at rest but goes to Bad when the toggle is activated that battery is bad. Now the dilema comes when 5 of the batteries test good and 1 is bad; do you replace all 6 or just 1? Bringing a new battery to a somewhat weak bank will likely shorten the life of that single battery. On the Golf Cart I have been replacing them 1 at a time and still have 2 that are six years old. Burt we are talking about a boat and the reliance on the batteries will be more critical that in a Golf Cart. How you may proceed will depend on how do you use the boat; if used for day sails and weekends you can replace 1 at a time but if you are going on long trips it would be best to replace all. I don't have the problem in the boat as I only have a small 2 battery house bank backed up by a generator.

 

[Davidasailor26]

I run a 36V Golf Cart with six 6V batteries and whenever it feels a sluggish I conduct an individual load test on each of the batteries and I usually find one battery in the group that is bad. The procedure is to fully charge them all and then disconnect them. Since you are running 12V you can remove the wires to the negative poles of each battery. A cheap load tester will do and one can be purchased at Walmarts or Harbor Freight. Connect the (+) and (-) to one of the batteries and it will give the actual voltage and show in a color scale whether OK, Weak, or Bad. The tester will have a toggle switch that when activated it will introduce a resistance or load to the current and the meter will show a drop in the voltage. If the needle show OK at rest but goes to Bad when the toggle is activated that battery is bad.

A load tester like that probably works OK for testing your batteries for golf cart use, but is less likely to be a good test for boat house batteries. The golf cart needs higher current for relatively short periods of time, more like what the tester is checking. A house bank doesn’t need the high current but does need high capacity. Maine Sail’s testing of such load testers is at Are Battery Conductance Testers Worth It? - Marine How To.

 

[Nodak7]

All the batteries in one bank do not degrade at the same rate. I run a 36V Golf Cart with six 6V batteries and whenever it feels a sluggish I conduct an individual load test on each of the batteries and I usually find one battery in the group that is bad. The procedure is to fully charge them all and then disconnect them. Since you are running 12V you can remove the wires to the negative poles of each battery. A cheap load tester will do and one can be purchased at Walmarts or Harbor Freight. Connect the (+) and (-) to one of the batteries and it will give the actual voltage and show in a color scale whether OK, Weak, or Bad. The tester will have a toggle switch that when activated it will introduce a resistance or load to the current and the meter will show a drop in the voltage. If the needle show OK at rest but goes to Bad when the toggle is activated that battery is bad. Now the dilema comes when 5 of the batteries test good and 1 is bad; do you replace all 6 or just 1? Bringing a new battery to a somewhat weak bank will likely shorten the life of that single battery. On the Golf Cart I have been replacing them 1 at a time and still have 2 that are six years old. Burt we are talking about a boat and the reliance on the batteries will be more critical that in a Golf Cart. How you may proceed will depend on how do you use the boat; if used for day sails and weekends you can replace 1 at a time but if you are going on long trips it would be best to replace all. I don't have the problem in the boat as I only have a small 2 battery house bank backed up by a generator.

Thanks for the good information Benny. We use our boat for long trips and anchor outs that require a reliable battery bank. Though it seems recently that has not been the case. I think right now I am leaning towards just replacing the bank. They have given me good service and it seems that, as you suggest and say "replacing one at a time" would just compromise the bank. I have gotten many more years out of them than I expected so I will just bite the bullet. We live in SW Florida and the heat here is tough on batteries plus we have a solar system that keeps them charging up. Thanks again!

 

[Nodak7]

A load tester like that probably works OK for testing your batteries for golf cart use, but is less likely to be a good test for boat house batteries. The golf cart needs higher current for relatively short periods of time, more like what the tester is checking. A house bank doesn’t need the high current but does need high capacity. Maine Sail’s testing of such load testers is at Are Battery Conductance Testers Worth It? - Marine How To.

Interesting article David. Thanks

 

[Tally Ho]

If I had a separate start battery, I would just continue to use the house back until it got to a point that it was obvious that they were on their last legs… if I had to rely on them to start my engine…I wouldn’t be quite so cavalier

Greg

 

[Terry Cox]

When I left on my cruise north into British Columbia the first part of July, the 12 year old dual 8D AGM house bank seemed to perform as normal. A charge down to a -20 AH would last for a couple of days until the next charge from the 8KW Genset. As time progressed I noticed that I had to run the Genset for a longer period of time and then the bank would not hold a charge for the two full days until the next recharge. It got so bad I had to turn off both reefers at night, otherwise the bank would be dead at less than 12 volts. I did manage to get home okay by running only the refrigerator and then turning it off at night. We now have two new 8D AGMs that should last for as long as we keep the boat, hopefully.

 

[Kings Gambit]

I have six (6) Trojan T105 6v Batteries for my house battery system. They have been in service for over 8 years now which is well beyond my expectations. I am a bit nervous regarding their age. The voltage shows good and the Specific Gravity is still good. The only point that concerns me is it seems the bank is running down faster overnight. Is there any other test I can do to determine condition? Or should I just bite the bullet and replace the bank since I got well over the normal bank life expectancy with them? Your thoughts?

Interesting. I’m experiencing the same problem with my house bank of similar age. Four six-volt batteries wired in series parallel. On my cruise in September of 14 days from services (shore power) I found it increasing difficult to keep up the batteries in the last few days. They did not charge up as fully as when newer. I resorted to charging with my Balmar high output alternator for 30 min at six-hr intervals to keep voltage above 12.2 the last day and a half, despite having my solar panels working most of the days. The batteries seemed not to be accepting the charging, and then losing the charge they had in short period.

We quit the anchorage at Santa Cruz Island two days earlier than planned to return to harbor (Channel Islands) concerned over running them down too low. On shore power two nights, then 60 n.mi. motor back to Long Beach, and then back on shore power (SmartCharger) since. After letting them lay disconnected from power for a couple of nights with nothing on, the voltage read 12.69. (I’ll do this again.) Yesterday, the hydrometer showed all cells in the GOOD range. So, I know they are old (6+ yr) and not up to snuff, but probably still good for weekend excursions, maybe 3 or 4 nights w/o trouble signs; but then maybe not either. As mentioned above, the on-going problem is diminished/degraded capacity which is onerous to measure correctly.