13.5 volts on the battery bank

[Canine]

When we got home last night,I went down to the power and water dept.(my shop)to turn the pump on and the battery bank was showing 13.5 volts.After dark.I have never seen this before.Is this possible or are my meters wrong?I thought a fully charged battery had about 12.7 volts.

 

[jimindenver]

surface charge, it will burn off.

 

[rvpopeye]

That's called surface charge , did you just finish charging???
The true voltage will show after putting a load on for a minute or so.

 

[Canine]

Well,the lights were on and the refrigerator was on but I don't know if it was running.No TVs or sat dish or other appliances on.It being a surface charge makes sense,I had just never saw it before.

 

[Spaceman Spiff]

My batteries (2 X GC2) have been showing a consistent 13+ volts on my Trimetric for most of the winter.  Solar charging with no load.  I think it is the cold weather.  Specific gravity was 1.300 (temp compensated) when I checked yesterday.  Air temp was 34F.

 -- Spiff

 

[karl]

Mine ( 2 - Trojan GC) regularly show a surface charge of 13+ til after dark if there isn't a load greater than my LED rope lights. It soon drops to 12.5 if the reefer and furnace kick on.

 

[SternWake]

With little to no load, surface charged can last for days.
Do note that if these batteries are not cycled, they should not be held at absorption voltage for hours each day, like if they were cycled

 

[Canine]

Vic did 3 loads of clothes today and ran the dishwasher.She is watching tv and the refrigerator is on.I just looked and the batteries are showing 12.5 volt.I didn't check the SG.Guess everything is back to normal.I'll check the water level and SG tomorrow.When we left 6 weeks or so ago,we only left the refrigerator and security lights on.Maybe that caused the voltage spike.

 

[Spaceman Spiff]

Do note that if these batteries are not cycled, they should not be held at absorption voltage for hours each day, like if they were cycled

So how should batteries be stored if they are not used for a period of time?

-- Spiff

 

[SternWake]

So how should batteries be stored if they are not used for a period of time?

-- Spiff

Depends on the battery(s) and the charging options available.

My solar controller currently can be set for as little as 30 minutes of absorption voltage, but I can also set the amperage threshold.  When it takes only 0.4 amps to hold 14.5v, it reverts to 13.6v float voltage regardless of how much time has passed since the solar got the battery to 14.5v.

So if my battery was not discharged overnight, as soon as it took only 0.4 amps to hold 14.5v it would revert to the 13.6v my Northstar AGM specifies.  When this battery is fully charged, it takes very little to bring the battery to 14.4v, so shortly after sunrise, and it stays there till sundown.

Some dumb solar controllers will just do the egg timer thing, holding ~14.4v for 2.5 hours irregardless if the batteries need it or not.  This increases water usage and will contribute to positive plate shedding. 

If not using the batteries,  and no Solar, Disconnect negative cable, plug in to recharge monthly if possible.  No more than 3 months for flooded batteries, unless very cool.  Keep batteries as cool as possible when not in use.

Some utilize plug in maintainers.  Check voltage on these occassionally, make sure it does not drift, and that it meets your battery manufacturer recommendations as to float voltage.  Some of the cheapo maintainers can not regulate voltage very well, varying within the same product on the shelf by 0.5v, so some luck of the draw, as you do not want to float at 14.2, unless it is super cold.