Are my batteries shot? - SailNet Community
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Are my batteries shot?

I rush-produced a video of this, which may be more interesting than reading for some people: https://youtu.be/G31ICABzKhw

But, if you'd rather read, here's the skinny:

I inherited these batteries from the previous owner, so I don't know how well they've been cared for.

After getting my solar charging system working, I started doing some experimenting ... the solar seemed to be working fine, but I'm concerned by how the batteries are behaving.

After fully charging till the Victron goes to float, I turn off all charging and monitor the battery voltage over the course of about two hours. During this time, the only thing using the batteries is the refrigerator compressor, which pulls about 4.5 amps and runs about 30% of the time. A little math tells me that over 2 hours the fridge should draw less than 5 amp-hours.

After two hours the battery voltage is down to about 12.5v. These are flooded batteries, and from what I've found on the internet, 12.4v is about 75% ... so, I'm guessing they're down to about 85% or so.

But for 5 AH to be 85% I'd need to have a battery bank with only 35AH. This bank should have about 330 AH.

Did I do the math wrong somewhere? Or are these batteries just really wore out?
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Old 05-13-2019
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Re: Are my batteries shot?

I'll let others more knowledgeable about load testing to chime in, but I suspect this test isn't giving you an accurate assessment. What was the resting voltage after a "full" charge? What were the SGs of the each cell? A number of ways to determine the health of the batteries.

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Old 05-13-2019
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Re: Are my batteries shot?

Likely yes. But if you want greater precision, you should get an ammeter and voltmeter.

Quote:
Originally Posted by BillMoran View Post
After fully charging till the Victron goes to float
Do not assume that one means the other.

Ideally test on shore power, isolated from all loads.

Confirm the V Absorb setpoint is at the high end of the batt mfg spec. Start a new cycle and observe what Amps are when it transitions to Float. Repeat until amps are either dropped to 1-2A, or does not drop at all for an hour.

That means they're now as 100% Full as they'll get, even if aged.

Now watching volts, apply a steady load of 15A and start a timer. Ideally adjustable, as voltage drops you'll need to the power to keep Amps constant.

Stop when volts hits 10.5V, that's 0% SoC

Supposed to be 20 hours. Anything below 14 hours, replace. 16 hours might get a little more use out of them.

For more details, search for

20 hour capacity test

here https://marinehowto.com/programming-a-battery-monitor/

Better yet read it all, *and check out the rest of the site.
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Old 05-13-2019
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Re: Are my batteries shot?

Get them fully charged remember getting the last 20 % in takes time.

Let them stand for at least 3 days and a week is better.

Apply a known load ideally 10 % of nominal capacity for 3 hours. Measure the voltage. If you are OCD you can graph the output voltage by measuring the voltage every 15 minutes.

12.5 volts and you are golden

12.4 is reasonable

12.2 well they have some life left

12.0 or less and they are done.
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Re: Are my batteries shot?

How does your battery charger know to switch from Absorb to Float?

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Re: Are my batteries shot?

Quote:
Originally Posted by Minnewaska View Post
How does your battery charger know to switch from Absorb to Float?
Huh ... beats the fleas out of me.

It's a Victron SmartSolar ... anyone know how these operate?
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Old 05-14-2019
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Re: Are my batteries shot?

My guess is, you're not actually topping the batteries off. Voltage, especially under load, is an inaccurate way to measure capacity or State of Charge. Just getting a lead acid battery up to max charge voltage, is simply the switch from Bulk to Absorb stage. You also want to know this is the correct voltage for your battery chemistry (flood, agm, gel, etc) They can still have 20ish percent of capacity left to charge in Absorb. The only way I know to do this accurately is with a shunt and the ability to monitor the amount of charge amps being accepted by the batteries, not what's being provided by the charge source, which is also being used to satisfy simultaneous loads.

Solar is great, but it may not simply have the amps, time or sunlight to get you all the way to full anyway. That depends on a lot of factors.

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Re: Are my batteries shot?

You don't know the history of the batteries. But you can bet that they have "lost capacity"... which is inevitable as batteries go through discharge and recharge cycles. And the deeper the discharge and recharge... the shorter their service life. One sign of old batteries is that they stop taking charge after a relatively short period when they are being charged from a discharged state. Old batts will reach "full" rather quickly and then discharge rather quickly... their capacity is shot.

Although expensive you should get yourself some new batts and set up a reliable monitor and charging system with smart regulators. If you have some alt charging... such as solar you should be able to keep the bank topped up unless you are a using too many amps.

This means you'll want to use power sparingly and change your lamping to LEDs...

You will not get an old horse to act like a young one... no matter what crop you use.

pay attention... someone's life depends on it
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Re: Are my batteries shot?

Quote:
Originally Posted by BillMoran View Post
It's a Victron SmartSolar ... anyone know how these operate?
http://www.cruisersforum.com/forums/...hm-202526.html
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Re: Are my batteries shot?

I didn't read the whole thread, but did read the explanation of how the controller works. My layman's recap...... it guesses better than most other timer style chargers. In the end, you don't know your bank is actually full. Further, it sounds like the user still needs to setup the charge voltages correctly.

My old charger held Absorb for a preset amount of time. No more, no less, everytime. That was awful.

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