Topping off lead-acid battery

Electrical and electronic topics for small boats
Oldslowandugly
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Topping off lead-acid battery

Postby Oldslowandugly » Mon Aug 24, 2020 8:52 pm

I use a Sears deep cycle lead-acid battery for starting and accessories on my fifteen footer. The hot summer days tend to evaporate a lot of the battery water. I am convinced some acid also leaves with the water vapor. Normally I just top off with distilled water. But I feel that dilutes the acid and the battery eventually can't hold a good charge. I started adding a 25% acid/ 75% distilled water mix to top off. By doing that I am finding that the battery charges back up very fast even if it was very low and it needed a lot. When I added just water it took a long time to re-charge. I don't know what the concentration of acid should be. Can I hurt the battery if it is too acidic?

jimh
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Re: Topping off lead-acid battery

Postby jimh » Tue Aug 25, 2020 6:56 am

What specific acid are you adding?

What strength is the acid?

And where do you buy it?

As long as you add Sulfuric Acid and you dilute it 1:3 with water, I can’t see any harm being done.

Jefecinco
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Re: Topping off lead-acid battery

Postby Jefecinco » Tue Aug 25, 2020 10:44 am

The way to check the battery acid concentration is by checking the specific gravity reading of the cells at full charge. I don't remember the desired concentration but a little research will tell you. When using large battery banks in power plants specific gravity was constantly monitored with a hygrometer and adjusted as needed. When a battery is discharged the specific gravity changes because much of the acid is stored in the plates. Charging returns the acid to the solution.

I believe adding acid before charging and checking specific gravity may, at best, shorten battery life. Batteries can explode spontaneously. That can lead to large insurance claims.
Butch

Jefecinco
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Joined: Fri Oct 09, 2015 6:35 pm
Location: Gulf Shores, AL

Re: Topping off lead-acid battery

Postby Jefecinco » Tue Aug 25, 2020 10:45 am

The way to check the battery acid concentration is by checking the specific gravity reading of the cells at full charge. I don't remember the desired concentration but a little research will tell you. When using large battery banks in power plants specific gravity was constantly monitored with a hygrometer and adjusted as needed. When a battery is discharged the specific gravity changes because much of the acid is stored in the plates. Charging returns the acid to the solution.

I believe adding acid before charging and checking specific gravity may, at best, shorten battery life. Batteries can explode spontaneously. That can lead to large insurance claims.
Butch

Oldslowandugly
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Joined: Fri Jan 15, 2016 11:19 pm
Location: Queens NY

Re: Topping off lead-acid battery

Postby Oldslowandugly » Tue Aug 25, 2020 11:19 am

I added sulfuric battery acid I bought at Advance Auto Parts. I tossed the box but the concentration was what you would add to a new dry battery. I always thought the hydrometer measured the state of charge, not the acid concentration. Or is that the same thing?

Jefecinco
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Joined: Fri Oct 09, 2015 6:35 pm
Location: Gulf Shores, AL

Re: Topping off lead-acid battery

Postby Jefecinco » Thu Aug 27, 2020 11:08 am

The acid to water ratio will depend upon the state of charge . A hygrometer is a useful device to determine that. A problem with using a voltmeter to determine state of charge is that to get an accurate reading all devices connected to the battery should be disconnected as many devices consume power when switched off. If the battery is connected via an on/off switch disconnecting may not be necessary for accuracy.

The downside of a hygrometer is that it is useless with sealed batteries and it's use requires some room to use it. Of course if a battery is sealed acid cannot be added so that make it moot.

Bottom line is that acid should not be added to batteries. How do you determine how much is enough? I suspect acid in electrolyte does not evaporate. It can boil out if a battery is overcharged. In that case electrolyte could be added but not just acid.
Butch