Battery question

[drb9]

I have a 12v deep cycle battery that is currently reading 16v. It's four years old, so I imagine it needs replacing, but can anyone surmise why it reads too high instead of too low. (My second deep cycle, same age, reads 10.4v. Definitely needs replacing.)

[Larry DeMers]

I have a 12v deep cycle battery that is currently reading 16v. It's four years old, so I imagine it needs replacing, but can anyone surmise why it reads too high instead of too low. (My second deep cycle, same age, reads 10.4v. Definitely needs replacing.)

There is no way for a 12v DC battery to read 16v without an outside voltage source being applied. In other words, is the charger on while you were measuring this voltage? Sounds like one battery is being charged too highly, and the other is over discharged.
I would suggest that you check the battery charger, and turn it off. Then a few hours later, remeasure that batteries voltage and compare it to the other battery.

In no case should the voltage reach 16v except when you are trying to equalize the cells in that battery, and this is usually for an 8 hour period only.

So what kind of charger do you have? What do you have in the charging circuit? (ie: charge combiner, diodes,etc) More info please.

[Ed Haley]

I have an RV motorhome that's been stored all winter with the batteries in the engine compartment but with both + and - terminals disconnected on both the house battery and the engine battery. After 4 months of storage, I went to the batteries to check on them. Before I connected the terminals on the batteries I measured the voltage on each battery with a voltmeter. Both batteries measured 16.3 volts. Nothing was connected to the terminals and water levels were appropriate.

I connected the batteries to their appropriate terminals and went to start the RV. With less that 1/2 second of starter engagement the engine started up and ran w/o assistance. I was pleased.

I, too, was surprised at the 16+ volts. The house battery, a top of the line deep discharge type, was new last spring and the engine battery was in the RV when I bought it. It must be about 4 years old.

[drb9]

I pulled the batteries from the boat last fall, and stored them in my shed over the winter, charging them about every 6 weeks with a portable automatic battery charger. Most recently, I charged each of them for a few days, then unplugged them from the charger and let them sit for a week. I used a voltmeter to check the voltage, and that's when I got the readings. I thought maybe the voltmeter was malfunctioning, so I hooked it up to a AA battery, which read 1.5v. So, I'm still puzzled. It could be the charger, but I don't know why a battery would hold the high charge after a few days even if it were overcharged.

In some ways, I don't really care, because I'm going to replace both batteries anyway. I got the originals at Costco for $48 each, and they lasted 4 years, so I'll get a new set there as well.

[drb9]

Ed, I'm concerned that I might do some damage to electronics if I run 16v through them. Do you have that concern about your batteries?

[Ed Haley]

I have no idea why the 16+ volts are present but when operating the vehicle I never saw voltage higher than about 12.6 volts. I'm not an electronics guru as Larry is but it may have something to do with the batteries just sitting around doing nothing.

BTW, I never charged the batteries while the RV was being stored. That's the voltage after a winter of not being touched.

I'm not worried about the 16 volts being applied to the RV. On Mokita, a lot of the electronics indicate voltages of between 10 and 20 volts would safely operate them. Heck, solar cells have a high output of over 16 volts. My Garmin 48 GPS can use voltages from 10 to 32 volts. You'll have to check your electronic specification data for your appliances to see what the useable voltage range might be.

I'm sure your batteries are functioning OK. They may not put out the amps they did when they were new. But you'll be able to tell when you try to start your engine.

[Oswego John]

Hi Ed, drb9 and Larry

For as long as I can remember, there was an oft quoted saying. "BATTERIES NEVER DIE, THEY ARE MURDERED". Just the other day, I recently reread that saying on a battery website. Let me give some thoughts on the battery voltage issue.

First off, I'll never argue with Larry when it comes to batteries. He made a nice living for many years doing what battery engineers do.
Larry's the man. If you reread his post, he did give us some clues.

There is a lot going on inside of that battery case. There's a lot of electrochemistry happening. Also a lot of variables to consider, number of plates, area of plates, thickness of plates, material of plates, type of battery, type of electrolyte, etc, and the beat goes on.

I met with two other geezers for coffee today and I mentioned the high battery voltage situation. One of the guys had an automotive electric shop for many years and the other worked in a shipyard until he retired. Both of them offered the initial response that the voltage tester was defective. After some discussion, other thoughts arose.

I have personally seen a 12 volt (nominal) battery measure over 14 volts. I haven't seen anywhere near 16 volts. Consider what the average domestic battery charger is. First, it is a stepdown transformer. For all practical purposes, it should be noted that you transform AC voltage, not DC. Then the lowered AC voltage, arguably 13 volts AC (lets not consider any other losses at this time) is rectified to 13 volts DC +/-.

What might affect the battery's voltage? Some thoughts.
Using the same voltmeter, after it being tested for accuracy:

Are there any extension cords used to power the charger?
What is the charger's input AC voltage?
What is the charger's output DC voltage?
Is the charger a multi voltage charger? 6V-12V output
What is the AC voltage of the power source? Remember that the xformer ratio remains the same, no matter what the input AC voltage might be, 108v, 112v, 115v, 120v, 122v, whatever. It will directly influence the DC output voltage.

Without any definite knowledge, it had been suggested that a newer battery with little or no lead sulfate on the plates, fully charged, could in time have a temporary higher voltage. Subjecting the battery to a load for a short duration would quickly return the voltage to a more normal reading.

There is a wealth of DC battery info to be had at

http://www.dcbattery.com/faq.html

Pay attention to questions:
#5 - deep cycle batteries
#7 - overcharging.
#8 - overdischarging.

FWIW
O J

[Leo MacDonald]

Hi drb9,

As Larry and OJ said, a steady state lead acid wet cell battery will NEVER read 16 VDC, NEVER.

Possible explanations;

1. 'Radio Shack' (or equivalent) moving vane 'multimeter'. (I use a 'Fluke' digital multimeter.)

2. Over-charging. During most 3 stage charging cycles the most you should see is ~14.4 VDC. When 'Equalizing' (once per year and very controlled - NOT to be done until you fully understand why and what this does) maybe in the 15.4 VDC area. (E.L. has a 'Heart-Interface '3 stage regulator for the engine alternator and a 'True Charger-20' for shore power battery charging.)

Recommend reading some Ample Power , Balmar, Blue Sea Primers on Shipboard electrics, installing a 3 stage battery charger and a good quality digital multimeter. All BEFORE installing the new batteries

Let us know how this works out. And post additional questions.

[Larry DeMers]

I have a 12v deep cycle battery that is currently reading 16v. It's four years old, so I imagine it needs replacing, but can anyone surmise why it reads too high instead of too low. (My second deep cycle, same age, reads 10.4v. Definitely needs replacing.)

Hi Guys,

I'm wondering if when the voltage measurement was done, there might have been some corrosion or battery acid "white stuff" on the battery posts? I have seen a voltage measurement go awry when the probe was not pushed down into the battery terminal, allowing a bit of corrosion to remain between the probe and the terminal. This forms a "local cell" which may raise the voltage measured. Clean the contact area, then assure a good connection for the reading. I bet it changes then, down to a more likely 12v +/-.

Cheers,

[Ed Haley]

In my case, it may have been a weak battery in the volt meter. I changed the battery and went to the dealer where I bought the Optima battery and it tested 12.65 v. on the shelf. When I went to the RV and checked the starting battery it was 12.4 volts.

Even though the Optima initially checked out at 16.3 v. I still suspected something wrong especially when Larry indicated a problem somewhere. I should have figured it was the voltmeter when "both" batteries had readings over 16 v.

When charging, the RV registers 14.2 volts so I'm happy to have the problem solved with a battery replacement for the voltmeter

[nikon4004]

Remember, a battery tested without a load applied will read high. 16 is a bit excessive,a dnI'd be suspect of the volt meter. Take the battery to an auto part store and they with check and cycle the battery for free.


Steve
Boatless in Ohio, but not for long!

[Ed Haley]

Just to be sure, I took the battery back where I bought it (Advance Auto) and they checked it out for me for free. It turns out the battery was defective. They couldn't tell me what the problem was (or else couldn't understand the codes) since the tester merely outputs a code and whether it's good or bad. And this $170. battery was bad. I still had 18 days left on the warranty so they gave me a new battery - no problem.

John Dunn is right about some of the advice on this board - it's better than technology.