Termination voltage for new deep cycle battery?

I have a new Walmart 27-series deep cycle battery, maybe 2 months old and working fine. I charge it religiously immediately after every trip with my 2/10/30 amp smartcharger.

I installed a small voltmeter in my battery box to help me keep a closer eye on the remaining charge. I've noticed that after the charger says it is "full" and stops charging the voltmeter reports 13.0 volts. Is that the right termination voltage for a new battery or should it be a little higher? I understand about surface charge but still thought it should be higher. :dono

Battery voltages

Attachment 167306

Does that mean I have 80% capacity left if my voltmeter shows 12.4v under load or at rest?

At rest or no load on the battery.

I have read recently that the only true way to determine if the battery is at full charge is to test it with a hygrometer....the old school way.
It seems that almost none of the modern automatic chargers will fully charge a battery.......To get a full charge, a trickle charger must be attached after the automatic charger is done and charge til the hygrometer shows a full charge......or just do that once and know how long it takes on the trickle charge.

A hygrometer use to be the best way before the digital meters were invented. Its pretty hard to read tenths of a volt on an analog meter.

Bob, yes, I have resorted to switching over to the trickle charger afterwards but this only increased the resting voltage a tenth or two.

Quote:

---

Originally Posted by Barnacle Bill

At rest or no load on the battery.

---

Bill,

What does it mean then if under load the battery eventually drains down to something like 11.4v? It probably will go back up to something like a resting 11.7 or 11.9 volts? Is it Ok to run it into the lower 11v range if it goes back up to the ranges shown on your graphic at rest?

Its normal for the voltage to go down when the battery is under a load (being used). As long as it charges back up fully and stays there when not being used you are good to go. If you have any doubts about it take it to your local auto parts store and have them test it. Its free and then you will know for sure. They have some amazing equipment for testing batteries nowadays.

If the battery doesn't get back to a full charge, the life of the battery will be reduced.