Curiosity Battery Question

[sailorboy1]

Just a curiosity question about my old T105 batteries.

I had 2 sets of them wired in standard series/parallel for 6V golf cart batteries to make a 440AH 12V house bank. Shorty after a solar charging issue while I was away that drained the batteries, they started always accepting a lot more amps after reaching 100% than in the past. They had always tapered down to 1-2% (4-8 amps) of C20 as they hit 100% at 14.8V. But after the solar problem they would accept 20-25 amps at 100% and 14.8V.

This went on for a couple of months and everything else seemed the same as in the past. But finally one evening my wife walks across the salon and says the sole is warm above one set. That set was pretty warm and almost hot and it had been an hour since the sun had gone down. So I took that set out of the bank and ran on just the other for a while till I could get to replacing (all of them).

Now those batteries capacity seemed fine. The morning battery voltages were same as always, so the capacity appears to not been reduced to a degree that I could tell. They just never seemed to get fully charged to point that internal resistance cut down the amperage as much as expected and based on experience. That suggests to me that the internal resistance was lower now and I would have thought that would affect capacity and self discharge. These batteries were disconnected for 3 months and when I pulled them I expected to see one of them discharged more than the other, i.e. I expected to find one that I could say was "bad". But they both measured about the same voltage and at near 100%.

There you go, spin some theories.

[Sailmonkey]

I had a theory until the last 2 sentences.

But our old batteries did the same thing as they neared end of life. The tail amps just never dropped. But the capacity was noticeably diminished

[a64pilot]

The internal resistance was actually higher, not lower, that’s where the power was going, into heat of course and not battery charging.
“Mud” that’s what the battery manufacturers call plate material that sheds and build up on the bottom can act as a partial short.
That’s one possibility, But of course usually a short will kill a battery once it’s no longer being charged, not always, but it’s what usually happens.

My old Lifeline bank (6 years) has degraded in capacity, confined initially by Smart Gauge, and also by Lifelines voltage under load SOC chart, but it still charges until .5% of rated capacity, just like it did when new, and if I wasn’t tracking the capacity I’d say they were still in perfect shape as there is plenty of reserve capacity to get me though overnight.

Point being is that I believe there are many, many banks in service that are actually dead, but as the low voltage alarm never goes off or there is enough battery to start the motor in the morning, people just keep driving on, average person doesn’t replace a bank until it completely fails, and I believe often that failure is an internal short and the first the average owner knows about it is the rotten egg smell that they track down to a hot, boiled dry battery.

Like an automobile, the battery is fine until one day it won’t start the car, then it’s dead, but in truth it’s likely been dead for at least a year.

I believe that never actually achieving a full charge is classic sulphation, as a battery sulphates it takes longer and longer to fully charge, eventually it takes forever, meaning of course it will never drop in absorption amps to be called fully charged

On edit
I’ve talked to many people, and it seems that on average, people that actually cruise at least half the year cycling their bank every day seem to get an average bank life of roughly 5 or 6 years, bank chemistry doesn’t seem to factory into it much and it would seem that “premium” batteries don’t actually do all that much better either.
That of course goes completely against what many often report here, and I can’t explain why or how some may get a decade or more out of a bank, when the average cruiser I’ve talked to kills them at 5 years.

[Bill O]

Originally Posted by a64pilot

The internal resistance was actually higher, not lower, that’s where the power was going, into heat of course and not battery charging.
“Mud” that’s what the battery manufacturers call plate material that sheds and build up on the bottom can act as a partial short.
That’s one possibility, But of course usually a short will kill a battery once it’s no longer being charged, not always, but it’s what usually happens.

My old Lifeline bank (6 years) has degraded in capacity, confined initially by Smart Gauge, and also by Lifelines voltage under load SOC chart, but it still charges until .5% of rated capacity, just like it did when new, and if I wasn’t tracking the capacity I’d say they were still in perfect shape as there is plenty of reserve capacity to get me though overnight.

Point being is that I believe there are many, many banks in service that are actually dead, but as the low voltage alarm never goes off or there is enough battery to start the motor in the morning, people just keep driving on, average person doesn’t replace a bank until it completely fails, and I believe often that failure is an internal short and the first the average owner knows about it is the rotten egg smell that they track down to a hot, boiled dry battery.

Like an automobile, the battery is fine until one day it won’t start the car, then it’s dead, but in truth it’s likely been dead for at least a year.

I believe that never actually achieving a full charge is classic sulphation, as a battery sulphates it takes longer and longer to fully charge, eventually it takes forever, meaning of course it will never drop in absorption amps to be called fully charged

On edit
I’ve talked to many people, and it seems that on average, people that actually cruise at least half the year cycling their bank every day seem to get an average bank life of roughly 5 or 6 years, bank chemistry doesn’t seem to factory into it much and it would seem that “premium” batteries don’t actually do all that much better either.
That of course goes completely against what many often report here, and I can’t explain why or how some may get a decade or more out of a bank, when the average cruiser I’ve talked to kills them at 5 years.

+1. Nailed it, including observation in the edit! Sure others will have their theories, but this is on the money.