Battery Loses Charge

Electrical and electronic topics for small boats
Buoy
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Battery Loses Charge

Postby Buoy » Fri Apr 21, 2017 6:57 pm

[My boat has] a single battery and no battery switch. The battery loses its charge overnight almost completely as if I left the lights or radio on, and replacing the battery with another battery yields the same result.

So it seems something is draining the battery. I'd like to know if anyone has experienced this concern before. And if so, where and how to start troubleshooting the [cause]. I have an Ohmmeter and a testing lamp. Any advice is appreciated.

Thank you.
Last edited by Buoy on Tue May 02, 2017 7:26 pm, edited 2 times in total.

Acseatsri
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Re: Battery Loses Charge Overnight

Postby Acseatsri » Fri Apr 21, 2017 7:13 pm

What kind of boat? What accessories and electronics? Did this just start happening recently? Anything else you could add to point us in the right direction? First place I would look is the bilge pump or automatic switch could be stuck or partially shorting out.

jimh
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Re: Battery Loses Charge Overnight

Postby jimh » Fri Apr 21, 2017 7:34 pm

Lead-acid storage batteries store electrical energy, and if there is a discharge current, the stored energy will be consumed. The stored energy is measured in Ampere-hours. One Ampere discharge for one hour equals 1-Ampere-hour of energy discharged.

An "overnight" is roughly 12 hours. A typical marine lead-acid battery used in a small boat has storage for perhaps 50-Ampere-hours of electrical energy. If we assume that a battery was at full charge and had 50-Ampere-hours of stored energy, for the battery to be completely discharged in 12-hours suggests that the discharge current must have been 50/12 = 4.15-Amperes.

Look for some load on the battery that is consuming 4.15-Amperes. That is the only sort of discharge that could consume the typical 50-Ampere-hours of stored charge in the typical marine battery for a small boat in one overnight period. A load that is consuming 4.15-Amperes should be easy to find.

An Ohmmeter is not the best instrument for investigation of discharge currents. Insert an Ammeter in the circuit. Measure the discharge current at the battery positive terminal. To discover the load causing the discharge, disconnect various loads until the load discharging the current is identified.

To get better advice, please give the Ampere-hour capacity of the battery, the battery terminal voltage at onset of darkness, and the battery terminal voltage at the next period of daylight.

Ltsimp
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Re: Battery Loses Charge Overnight

Postby Ltsimp » Mon Apr 24, 2017 8:20 am

Sorry to hear of your problem. I would suggest starting with a simple test. Disconnect the battery from the boat, fully charge it and then load test the battery. If you do not have access to a load tester see if it still loses the charge overnight while disconnected. If it fails either of these simple tests then you need a new battery. If it passes, reconnect it to boat and begin isolating circuits by either turning off breakers or disconnecting wires 1 circuit at a time until you find the offending circuit. Good luck.

jimh
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Re: Battery Loses Charge Overnight

Postby jimh » Mon Apr 24, 2017 10:19 am

Buoy wrote:...replacing the battery with another battery yields the same result.


This tends to contraindicate the original battery as the cause of the discharge.

Buoy
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Location: Long Island

Re: Battery Loses Charge Overnight

Postby Buoy » Mon Apr 24, 2017 6:28 pm

Thanks all. The boat has been on land and I did not notice that the bilge pump had not been working. I started going thru all of the bilge float and bilge pump wire connections and found that some connections were corroded. I made three new connections using new connectors and shrink tubing, and still the pump is failing, both directly from the switch and via the automatic float.

Today, I replaced the 5-Ampere push-button circuit breaker,and the pump is now working.Woo hoo!

I'll continue the battery load testing when it stops raining. Thanks again for sharing your thoughts, I appreciate it.

jimh
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Re: Battery Loses Charge Overnight

Postby jimh » Wed Apr 26, 2017 8:01 am

On the somewhat corollary topic of sump pump wiring and how it relates to battery charge management: on my boat I have the aft livewell sump pump circuit wired directly to the battery so that the circuit can remain energized even when the primary DC power switch has been moved to the OFF position and all other loads are disconnected from the battery. (The aft live well is the lowest point on the boat where water can collect from rain water coming into the cockpit.) But the sump pump circuit is also controlled by a three-position switch. If automatic operation of the sump pump is desired while the boat is unattended and all other loads to the battery are switched off by the primary power switch setting, the sump pump control must be moved to the AUTO position from the OFF position. This will allow the pump to run under the control of its float switch. By setting this control switch for the sump pump to the OFF position, then all loads are disconnected from the battery.

Buoy
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Location: Long Island

Re: Battery Loses Charge Overnight

Postby Buoy » Thu Apr 27, 2017 1:17 pm

Last night the battery was showing a [terminal voltage] of 12.4-Volts and this morning it was 12.0-Volts, perhaps due to the rain we had overnight. It appears that the battery is no longer losing a significant amount of its charge. I assume the overnight decrease of 0.4-Volts is acceptable given the bilge pump had been running intermittently through the night. Thanks again.

jimh
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Re: Battery Loses Charge Overnight

Postby jimh » Thu Apr 27, 2017 6:19 pm

To better understand how a 12-Volt battery's terminal voltage correlates to state of charge, see the table at

Battery Charge
http://continuouswave.com/whaler/refere ... ttery.html

To understand how state of charge correlates to consumed energy, you have to know the Ampere-hour capacity of the battery, the initial state of charge, the amount of current in Amperes and the duration in hours of the discharge. You can then compute the amount of energy that was drained from the battery in terms of percentage of the stored energy that was initially in the battery.

In your narrative you only provide an initial terminal voltage and an ending terminal voltage. This won't be enough information to calculate if the discharge that has occurred meets your criterion of "acceptable."