Nominal voltage of golf cart batts

[OldManMirage]

I have a set of 6volt batts coming out of my mother-in-law's golf cart. I'd like to use a pair of them to go ahead and set up my system on my boat. This will let me go ahead and get rid of some excess wiring at the same time.

Since I don't want to put them in there if they are totally shot, my question is what should the voltage be when fully charged at rest ?

I have disconnected them from each other - after charging them. I'm getting right at 6.5 volts, plus or minus .01v.

I can't find any specs for this particular battery - Powertron P2000 6V Deep Cycle.

A website I came across said GC batts should read 6.37 when full. That doesn't seem right.

Appreciate any insight here.
Thanks !

[thomm225]

Sounds pretty close though to correct.

Mine which are hooked up in series read about 12.6 volts a couple days after charging.

I've been disconnecting them from the controller and panel after absorption phase ends.

They are 6 volt Season All Golf Cart Batteries 220 ah.

https://www.batteriesplus.com/produc...y/sligc2d06220

[Bill O]

How about testing the individual cells w/a hydrometer instead?

[Jim Cate]

Resting voltage does not tell you much about capacity and is highly temperature dependent.

The best means of determining the A-H capacity is to charge at absorbtion voltage until the current drops to ~ 1 % of the nominal capacity in A-H and then discharge at 20 A until the voltage drops to 5.25 (for a typical GC battery). The length of time to reach that voltage times 20 is the capacity in A-H.

If the batteries have been discarded for golf cart usage I doubt if there is much life left in them for boat use... but who knows how picky the golfer is about such things!

Jim

[thomm225]

As usual some are overthinking a simple check.

The 6.37 volts is fine. If you want more info than that you’ll have to test them more extensively or simply install them and see.

I installed mine in maybe 20 minutes.

On the other hand, my two golf cart batteries were less than $300 for both. They are 220ah

[boatpoker]

Originally Posted by Jim Cate

Resting voltage does not tell you much about capacity and is highly temperature dependent.

The best means of determining the A-H capacity is to charge at absorbtion voltage until the current drops to ~ 1 % of the nominal capacity in A-H and then discharge at 20 A until the voltage drops to 5.25 (for a typical GC battery). The length of time to reach that voltage times 20 is the capacity in A-H.

If the batteries have been discarded for golf cart usage I doubt if there is much life left in them for boat use... but who knows how picky the golfer is about such things!

Jim

This is the only way to know for sure.

[chris mac]

Jim's suggestion Is the best way to know how usable the batteries are for a house bank.
Since this sounds like your first (or close to) step into 12 volt setup, these batteries might be an ok experiment for you. Each brand is slightly different, my gc are full at 12.7 and 50% at 12.2.(in series) So as long as you keep them somewhere between, you will be fine running small loads like lights and the odd pump, things like that. Running them lower Will still power the lights, but hurts/shortens the life of the batteries
If you want to run a fridge, inverter, or rely on a bilge pump to work while not present, then I recomend following Jim's advice, or buying new batteries

[OldManMirage]

Well, I was hoping for a more definite answer based on voltage, but I get it. Basically I'm trying to decide if it's worth the effort to lug a pair down to the boat and sweat them into place. Where I have to put them it will NOT be easy!!! So I may just wait until I'm ready to fork out the dough for a new pair.

Although I am really curious. Wish I has a 12volt load sitting around the house here somewhere..hmmm...then I could test a pair and see...

[OldManMirage]

Just remembered I have a small trolling motor. Perfect.

[thomm225]

Originally Posted by OldManMirage

Well, I was hoping for a more definite answer based on voltage, but I get it. Basically I'm trying to decide if it's worth the effort to lug a pair down to the boat and sweat them into place. Where I have to put them it will NOT be easy!!! So I may just wait until I'm ready to fork out the dough for a new pair.

Although I am really curious. Wish I has a 12volt load sitting around the house here somewhere..hmmm...then I could test a pair and see...

That's not a bad idea to test where they are.

You could get your connection battery cable to put them in series then try to put them on a load similar to what you have onboard.

Plus maybe get your largest solar panel and your controller for charging and have a mini testing setup.

Then maybe hook your inverter to the batteries and load it up with various ac units around the house.

As far as simply going by the voltage checks, that's how we test our large UPS Units if we get a battery alarm.

They have 24-72 batteries (12 volt AGM UPS)

When we replace all the batteries that read below 12 volts that usually corrects the problem for a 1-2 years

These day though due to the cost of the systems they are protecting we are required to replace all UPS batteries every 5 years which is like 500 plus batteries. In the mean time if there is a failure, we go by voltage and replace as need

Which brings us back to which type sailor you are (can you deal with a failed battery for a few days or weeks), difficulty in replacing, and dollars in your pocket

[Wotname]

Originally Posted by Jim Cate

Resting voltage does not tell you much about capacity and is highly temperature dependent.

The best means of determining the A-H capacity is to charge at absorbtion voltage until the current drops to ~ 1 % of the nominal capacity in A-H and then discharge at 20 A until the voltage drops to 5.25 (for a typical GC battery). The length of time to reach that voltage times 20 is the capacity in A-H.

If the batteries have been discarded for golf cart usage I doubt if there is much life left in them for boat use... but who knows how picky the golfer is about such things!

Jim

This needs repeating!
I test a lot of batteries. I can show you 10 batteries that recently all had 'proper' resting voltages and yet only had around 30% of their rated capacity.

[Jim Cate]

Originally Posted by thomm225

As usual some are overthinking a simple check.

The 6.37 volts is fine. If you want more info than that you’ll have to test them more extensively or simply install them and see.

I installed mine in maybe 20 minutes.

On the other hand, my two golf cart batteries were less than $300 for both. They are 220ah

As usual, some are recommending a simple check which does not solve t he op's question as to suitability of the batteries for use on board... something that is related to their A-H capacity, not their resting voltage.

And for the OP: it is possible to do the capacity check at loads other than the standard 20 A value. Use anything that draws say between 5 and 30 A. The only thing is that it should be a constant amperage (or reasonably so) in order to calculate how many A-H you have drawn before the battery is fully discharged. The measured capacity will be different from the 20 A value, but will still give you a reasonable idea as to their usefulness. Nothing magic about the 20 A value, it is just a standard adopted by the industry for uniform reporting.

Have fun with your science experiment, and I hope the batts are useful!

Jim

[Wotname]

Originally Posted by OldManMirage

Well, I was hoping for a more definite answer based on voltage, but I get it. Basically I'm trying to decide if it's worth the effort to lug a pair down to the boat and sweat them into place. Where I have to put them it will NOT be easy!!! So I may just wait until I'm ready to fork out the dough for a new pair.

Although I am really curious. Wish I has a 12volt load sitting around the house here somewhere..hmmm...then I could test a pair and see...

Do you have access to the MIL golf cart?

A rough and ready 12V load can be cobbled together with a few car (auto) headlight bulbs.

[thomm225]

Originally Posted by Jim Cate

As usual, some are recommending a simple check which does not solve t he op's question as to suitability of the batteries for use on board... something that is related to their A-H capacity, not their resting voltage.


Jim

Not quite.

I was responding to his initial question.

The OP said 6.37 volts on a 6 volt battery that he had seen on the internet didn't seem right. I think I saw that same post on a forum page .....not this forum

My response was that it was a good voltage. There was no other recommendation involved as far as testing.

Speaking of testing though I like the offline setup OP was considering. You could do various loads either 12 volt or with an inverter ac loads. And charge the batteries with solar right there on your patio or whatever. Plug a fan in for cooling dc or ac fan depending on your test rig

My testing was always done onboard though as I always had two 12 volt batteries. I once had to troubleshoot a bad battery under way and ended up coming in on one.

This is why I plan to install a backup 100 ah 12 volt battery for my golf cart batteries.

[Wotname]

Originally Posted by Jim Cate

As usual, some are recommending a simple check which does not solve t he op's question as to suitability of the batteries for use on board... something that is related to their A-H capacity, not their resting voltage.

And for the OP: it is possible to do the capacity check at loads other than the standard 20 A value. Use anything that draws say between 5 and 30 A. The only thing is that it should be a constant amperage (or reasonably so) in order to calculate how many A-H you have drawn before the battery is fully discharged. The measured capacity will be different from the 20 A value, but will still give you a reasonable idea as to their usefulness. Nothing magic about the 20 A value, it is just a standard adopted by the industry for uniform reporting.

Have fun with your science experiment, and I hope the batts are useful!

Jim

It is not always easy to maintain a reasonably constant amperage but it doesn't matter too much. Most loads will maintain a constant resistance and thus the current will vary as the battery under test discharges. If you graph the current against time say every 15 or 30 minutes, the curve quickly becomes apparent and the area under the curve gives you the capacity of the battery.

As Jim says, it becomes fun science experiment.