Existing batteries are 5 yrs old 8D AGM's. after only running my ceiling fan for an hour or two they're discharged down to 12.5V from 13.5. I'm guessing they are nearing the end of their lifespan.How can I test to make sure the batteries are ready to replace? I've priced replacements between $450 for house brand batteries to $650 and beyond for lifelines which seem to be the premium battery choice.The $450 battery specs at 250 AH and weighs 170lbs.Lifelines are about the same. What should I look for? Don't mind spending the money if getting better quality in return.But if they're basically the same I can put the money somewhere else. Thanks

Check out Universal Batteries. I replaced my 10 year old Lifelines (awesome but expensive) with the UB 8D batteries for half the price. Even if they only last 5 years I will break even. We are now in our 4th year and they are still going strong.

Without the proper equipment it cannot be. There are battery dealers that have the equipment to do so, Interstate is one of many. Some auto parts stores have the equipment, with the gaining use of AGMs in the auto and motorcycle industries.Life expectancy varies greatly, with the majority being 5 to 8 years, but I have heard of and had a set that made, lasted 11+.Have the batteries ever been desulfated ? If not it may be possible to extend their service life by doing so.

A fully charged battery at rest 12.6V. The 13.5V you are seeing is a surface charge.

sh410 wrote:A fully charged battery at rest 12.6V. The 13.5V you are seeing is a surface charge.Great catch. :@

sh410 wrote:A fully charged battery at rest 12.6V. The 13.5V you are seeing is a surface charge.The full charge for a conventional battery at 80 F is 12.65 but for an AGM it typically is 12.8.YOu can't use that 13.5 "surface charge" number for anything, except maybe to assure yourself that something is charging the battery.An AGM at 12.5 is about 65-70% charged and might be "on the way out"if that happened over a short period with a light load.The other consideration, however, is that 13.5 is just a float voltage for an AGM. If the charging voltage never goes above that they might not be getting fully charged......ever.You need to check that out before sinking a **** load of money into new batteries.

How to choose new 8D house batteries. | Good Sam Community

30 Replies

Passin_Thru
Explorer
Aug 20, 2015
LOL! Let him spend his money. Good grief. I let mine go dead. Have for years. After all there are more than one. I ran a pair, 1 went dead after 4 years the other lasted 6 more years.
harold1946
Explorer
Aug 19, 2015
An amp hour rating of 200 is the same whether 6 or 12 volt.
Properly hooked up, series parallel, for each pair of 6 volt 225 AH batteries the usable AH is increased by each set. With each additional set the multiplier is 225.

With my example of 6 - 225 ah batteries the rating is 670 AH.
If it did not work this way anyone with 6 volt batteries would be limited to the rating of the two batteries. no sense in adding more.

The way it works.
A series connection will double the voltage, while maintaining the same capacity equal to the rating of the individual batteries.

A parallel connection will double the capacity while maintaining the same voltage.

A series/ parallel combination connection will double the voltage and double the capacity.
Bikeboy57
Explorer
Aug 19, 2015
Hang on, in comparing battery capacity the voltage must be taken into consideration. 200Ah at 6 volts is half of 200Ah at 12 v.

So if you take two six volt golf cart batteries rated at 225 Ah, you have 225 Ah at 12V, not 450 Ah.
harold1946
Explorer
Aug 19, 2015
wa8yxm wrote:
wa8yxm@gmail.com[/quopte]

12.6 is Fully Charged anyting over 13 is a surface charge left over from the converter running and should self dissapate in a matter of minutes.

So I'd say your batteries are still good.

That said you might wish (Depending on the physical dimensions) to consider ging to six volt pairs.. TWO REASONS

1: Cost: They tend to be cheaper than an 8D
2: Wrangling (Wresteling them in and out) each battery is about half the weight of the 8D

Power storage capacity is dang near identical so not a consideration.

NOTE: 8d is one of the reaons I cringe when somneone ask "Which is better Two 12's or 2 6's If the 12's are 8d.. well than that's it (2 8D = 4 GC-2)

Not necessarily.
My 12V 8D AGMs are 290 AH @ 20hr rate. Most GC2s are around 225 AH @ 20 hr rate.
It is not a question of better, rather higher AH rating. What one wants
4- GC2s = 450 AH. 6 = 670 AH.
My 2-8Ds =580 AH. 3 = 870 AH. = 200 more AH.
Once they are installed there is no need to remove them until time to replace.
wa8yxm
Explorer III
Aug 19, 2015
wa8yxm@gmail.com[/quopte]

12.6 is Fully Charged anyting over 13 is a surface charge left over from the converter running and should self dissapate in a matter of minutes.

So I'd say your batteries are still good.

That said you might wish (Depending on the physical dimensions) to consider ging to six volt pairs.. TWO REASONS

1: Cost: They tend to be cheaper than an 8D
2: Wrangling (Wresteling them in and out) each battery is about half the weight of the 8D

Power storage capacity is dang near identical so not a consideration.

NOTE: 8d is one of the reaons I cringe when somneone ask "Which is better Two 12's or 2 6's If the 12's are 8d.. well than that's it (2 8D = 4 GC-2)
wolfe10
Explorer
Aug 19, 2015
Perhaps a little explanation is needed.

Agree that 12.2 VDC is as low as you want to go. BUT, this is as measured with batteries AT REST-- no charging and no discharging for some period of time.

If you are monitoring voltage UNDER LOAD, it can be lower and still "come back up" to 12.2 when the load is turned off.

A little experience with loads and monitoring the voltage during and after turning off the load will help you with this.
behengold
Explorer
Aug 19, 2015
will do. no lower then 12.2v
harold1946
Explorer
Aug 18, 2015
I second Dons' opinion. Deep discharging is an invitation to problems. Even at 12.2 recharge asap.
pianotuna
Nomad III
Aug 18, 2015
behengold,

I'd stop at 12.2. 12 is too deep a discharge Do a conditioning charge first.
behengold
Explorer
Aug 18, 2015
I'll check to make sure the charger s set up correctly and then try to see how long it takes for them to discharge down to 12v.

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How to choose new 8D house batteries.

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