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Leaving batteries on charge for prolonged periods of time.


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Probably a dumb question but here goes. 

Just before lock down we came back from a few days away and I did what I normally do and put the house batteries on charge. It's a decent charger, galvanic isolated with multi step regulator etc (from memory I think it ends up in a sort of "maintenance state" or something like that). 

Ordinarily I remove the charger next time I go down knowing they are fully topped off... but...you know...COVID.

Any issues with it being sat on the charger for months at a time? Or should the multi-step regulator keep it all in good shape? Thoughts anyone? I could get someone to switch it off at the shore end if needed but not sure it's a problem?

BTW they are pretty new batteries, both same brand and 100 and something Ahrs each so they should be in good order to start with.

BTW2 being at home all day means I get a lot of time to worry about stuff I probably shouldn't worry about!

 

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I hope it's okay because I've got two C-Teks running out at the hangar. I had another charger on as well but as I couldn't establish it's maintenance ability so I disconnected it. I've just been told I'm allowed to do a maintenance run on the plane, no flying though :-(, so i'll check them out this week.

Luckily the boat has a very good solar system so thats not a worry

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Theoretically they can stay on a "maintenance" or "float" charge indefinitely.  In my experience though, I've seen batts prematurely die with this regime - over years though, not months. I'm not sure why this is. 

On my own boat I use shore power to run the fridge at the dock, but leave the batt charger off - solar keeps batts full. 

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1 hour ago, Knot Me... maybe said:

If you have a real good charger you'll be fine, most these days are smarter than the users.

 

We've been told this morning we can do short do not leave the circuit flights to keep currency but no more. But my medical fell off 3 weeks ago, bum!

Automatic extension of medicals and BFR's til 24th June is in place

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19 minutes ago, Island Time said:

In my experience though, I've seen batts prematurely die with this regime - over years though, not months. I'm not sure why this is. 

 

No temperature compensation in a hot boat would do that. 

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I’ve been plugged into shore power & charging 24/7 for years - the longest single stint being literally about 9 months whilst I was living outside NZ - and had no problems. But I was using professionally installed kit including Victron charger. I’ve had several Victron units over the years and I reckon they’re the real deal (although not cheap). 

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The batteries will last longer on than off.

Commercial and emergency battery back up systems sit on a charger of some sort permanently . Letting the charge drop and then running it back up is hard cycling, which has a finite number in any battery system.

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It's all a bit more complex.....as usual when it comes to batteries.
Firstly, keeping a trickle charge on a battery is good. Can't go wrong with that part. But that is not the end of the story.

Basically, it doesn't matter what you do, a Lead acid battery deteriorates in same way, even left fully charged. From the day the battery was born and accepted it's very first charge, the Chemical reaction that creates the Electrical energy, slowly eats away at the life of the plate. Also, once the plate voltage drops below 12.6V, the plates start to Sulphate.
Trickle charging will stop sulphation from happening. Trickle charging is at a very low current and lower voltage than a normal charge voltage, so you do not have issues with a battery getting hot or boiling.
BUT!!!!! Trickle charging does not mean the battery will remain in tip top health forever, being an eager slave just waiting to please the day the master switches on a load.

FLA is the one battery type that needs the most maintenance. FLA's need to have the Electrolyte levels monitored and topped up when needed. Having special caps fitted to Deep cycles will aid in keeping the levels maintained for longer.
But! in float charge, FLA's  suffer from Stratification. This is where the denser Acid in the Electrolyte drops to the bottom leaving only water at the top of the plates.
It is good practice once a month (ruffly, it's not critical to skip a month or two for some reason ) to apply an equalization charge which stirs the electrolyte up and also helps to balance charge across the cells.
This is why Gel cell batteries tend to be used in remote backup power sites. They don't experience stratification of the electrolyte and thus a cheaper charger can be used.

You may have noticed comments in the past about "surface charge". Trickle charging is when this issue tends to take place. 
A plate does not charge evenly when a current is applied. The charge starts from the surface and works its way into the depth of the plate. This is why a Battery takes time to charge. The Chemistry change has to work it's way into the depth of the plate. Sitting on a trickle charge for extended times does not mean the entire depth of the plate remains fully charged. Within the plate, the charge will start to decline and eventually the surface only holds a charge. Testing may show a fully charged battery. But if you place a load on the battery, it's charge will drop away quickly and the battery will be flat. So once a month, the battery really needs to be placed under a load for awhile to ensure the surface charge has been used up. Then the battery is placed under a full charge and once fully charged, placed under an equalisation charge. There are a few top end Chargers that do this automatically and this is where you discover why some chargers are damn expensive. They are also very clever.

However, even on a tickle charge, eventually the battery will still die. The plate material slowly breaks down and the chemistry can no longer be maintained.

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