Mixing Batteries

[gramos]

no not a cooking enquiry ....

I have just found 1 of 4x 75 amp batteries only showing 11.6 volts after 48 hours on a 15 amp mains charger , so have deduced that it is failing and will need replacement . my question is , can I replace one battery as the remaining 3 are in good condition , I dont want to just throw them all away apart from the cost , its just not good for the planet ! I am currently trying out an "Optimate 111 " on the dud battery but it has achieved nothing ,restoratively, yet .

[anjou]

Cant you revive it?
Depending on which type of battery, you can do things to it and save its life.

Im sure a battery guru will advise.

[btrayfors]

gramos,

How old are they? How do you know the remaining three are in "good condition"? BTW, just because the voltage after testing may be in the "good" range, i.e., 12.6 or higher, says NOTHING about the capacity of the battery....only it's state of charge (SOC).

Sounds like the first battery may have a bad cell or be otherwise compromised. Is it feasible to just use three batteries for awhile (are they all 12V??). This way, you'd (1) get a better idea about how healthy those three really are; and (2) help you with the decision to replace one or all of them.

Bill

[David M]

Have you measured the specific gravity of the electrolyte with a hydrometer after applying a full charge?

Generally speaking, all four batteries need to be replaced if all four batteries are older batteries because the old batteries can bring down a new battery.

If your charger has an equalizing feature, you could try that. It may help some.

You may also want to test each with a battery tester. The large commercial ones at Walmart, auto shops or other places that sell batteries are better than the portable battery testers.

[gramos]

+

Originally Posted by btrayfors

gramos,

How old are they? How do you know the remaining three are in "good condition"? BTW, just because the voltage after testing may be in the "good" range, i.e., 12.6 or higher, says NOTHING about the capacity of the battery....only it's state of charge (SOC).

Sounds like the first battery may have a bad cell or be otherwise compromised. Is it feasible to just use three batteries for awhile (are they all 12V??). This way, you'd (1) get a better idea about how healthy those three really are; and (2) help you with the decision to replace one or all of them.

Bill

Bill , thanks , they are all 4 years old and are sealed so no chance of a hydrometer test , unfortunately . the other 3 show v little voltage drop after 24 or 48 hours so I assume theyre ok . this one drops 1+ quickly . yes all 12 volt . I could use 3 batts , no problem , except shes on the hard till april , but i can use the mains charger to replenish . I would really rather not replace all , batteries are expensive here and the 3 are still performing well . I have 160 watts of solar power keeping them all sweet .

[gramos]

Originally Posted by David M

Have you measured the specific gravity of the electrolyte with a hydrometer after applying a full charge?

Generally speaking, all four batteries need to be replaced if all four batteries are older batteries because the old batteries can bring down a new battery.

If your charger has an equalizing feature, you could try that. It may help some.

You may also want to test each with a battery tester. The large commercial ones at Walmart, auto shops or other places that sell batteries are better than the portable battery testers.

thanks David ,

I have answered some of these questions in the previous post , but can you explain the equalising subject ? I have a 15 amp mains fed charger built in to the whole battery system , yes it could be bigger , but its there now ! no idea if it has an equaliser feature ?
I will check the condition of errant battery tomorrow which will have been 48 hours on the Optimate battery "restorer" which has some very good claims and reports ...

[btrayfors]

"All sealed"?? Are they AGMs? "No Maintenance" batteries? Gels??

Whatever type they may be, I'd be very reluctant to add a new battery to a 4-year old battery bank.

Better to run with just 3 batteries...work 'em hard, treat 'em right, and maybe they'll last another season.

Also, in the next 4 months or so you might find someone with a sophisticated battery tester (e.g., Midtronics Micro 500XL or MDX-650 or equivalent). That would give you a much better indication of the health of each individual battery.

By the way, I just completed some tests on four 13-year old gelled golf cart batteries, which spent 10 years in service on a sailboat (mostly tied to the dock) and the past three years in my basement where they were used for an 18-month battery testing project. One of the four still tests nearly 100% capacity. The other three all test in the 60-80% range. Interestingly, they all test pretty close to the values they had when I acquired them three years ago.

Bill

[gramos]

thanks Bill , sealed lead acid type , all four . how about fitting a 2 year old 60 amp battery in place of the weak one that I have sat on the bench fully charged , but non deep cycle ? gramos

[btrayfors]

gramos,

Flooded, AGM flat plate, AGM spirals, and Gelled batteries are all lead-acid.

I assume yours is a so-called "Maintenance-Free" battery, which is a flooded type. In general, this is a good type to AVOID using on a boat except, perhaps, for starting batteries.

Don't think I'd add a starting battery to the mix. Better to find out what you've really got first, through testing and/or use.

When you do get new batteries, it's a good idea to invest in a good charger with a capacity of at least 25% of the AH rating of the house battery bank. Larger if they're AGMs.

Bill

[barnakiel]

If one of 4 is dead just deliver it to the skip and do with the remaining 3.

Do NOT mix.

b.