Replacing my Interstate 12V Coach Batteries - considering 6V golf cart batteries

[SargeW]

Good conversation about batteries! One question though. I have six 6 volt Interstates as house batteries in the rig. After a year they are still working well and don't require much water (I check at least once a month). My Magnum charger has an equalization program, but I need to self start it.  I full time and camp in a variety of places and situations. What would be the recommended equalization cycle to keep them at peak condition?

 

[ZinLuvR]

Can't add much to the scientific part of batteries, but I can tell ya it pays to shop around.  I had 4 Lifeline 8D AGM's that needed to be replaced.  The cost is enough to make you faint.  I shopped and shopped, prices are all over the place.  I ended up going with the Trojan 8D's, installed, and saved about a grand for the 4. 

 

[Optimistic Paranoid]

Good conversation about batteries! One question though. I have six 6 volt Interstates as house batteries in the rig. After a year they are still working well and don't require much water (I check at least once a month). My Magnum charger has an equalization program, but I need to self start it.  I full time and camp in a variety of places and situations. What would be the recommended equalization cycle to keep them at peak condition?

Well, here's what Trojan has to say about it:

Equalizing

FLOODED BATTERIES ONLY

Equalizing is an overcharge performed on flooded lead acid batteries
after they have been fully charged.

It reverses the buildup of negative chemical effects like
stratification, a condition where acid concentration is greater at the
bottom of the battery than at the top. Equalizing also helps to remove
sulfate crystals that might have built up on the plates. If left
unchecked, this condition, called sulfation, will reduce the overall
capacity of the battery.

Many experts recommend that batteries be equalized periodically, ranging
anywhere from once a month to once or twice per year. However, Trojan
only recommends equalizing when low or wide ranging specific gravity
(>0.030) are detected after fully charging a battery.



*Step-By-Step Equalizing*

1. Verify the battery(s) are flooded type.
2. Remove all loads from the batteries.
3. Connect battery charger.
4. Set charger for the equalizing voltage /(See Table 2 in the Charging
    section). /If your charger doesn?t have an equalization mode, you
    can unplug the charger and re-plug it back in. This also will
    conduct the equalization charge.
5. Start charging batteries.
6. Batteries will begin gassing and bubbling vigorously.
7. Take specific gravity readings every hour.
8. Equalization is complete when specific gravity values no longer rise
    during the gassing stage.

 

[JoelP]

for a maintenance charge you need to size the panel for twice the typical self discharge rate. ( typically 1 to 2 % per month )
a minimal starting point is to take the battery Ah capacity and multiply by 1%, 2% is better but this example will be for 1%

so say you have a 12 Volt 100 Ah battery ( eg: Group 31 ),  1% is 1 Amp so you need ( 1 Amp * 12 Volts ) = 12 Watts of solar
however, due to location and panel efficiency we need to multiply by a correction factor of 2.

so we now have 12 * 2 = 24 Watts.  we round up to 30 W.

a 30 Watt "12 Volt" panel can be had for $45 US
and a low cost 10 Amp PWM controller for as little at $20 US

less than $100 and peace of mind..

just scale this for other capacities..


for Amazon buyers..

https://www.amazon.com/HQST-Regulator-Charge-Controller-Display/dp/B01F5WFK5C
https://www.amazon.com/HQST-12Volt-Polycrystalline-Portable-Marine/dp/B072B5J7CF/ref=sr_1_5?s=automotive&ie=UTF8&qid=1533125754&sr=1-5&keywords=30+watt+solar+panel

Thanks Solarman for your reply.  I now have two 6 volt Deka batteries that are each labeled :75Amp rating 120 min.  I would assume that this means they could together deliver 75W for 240 minutes when in optimum condition.  In your nomenclaturee it would seem to me that these are 150 amp hr batteries, and together these to could deliver 300 amp hours. 1% would be 3 amps and 2% 6 amps. 6 amps at 12 volts would mean 72 watts.  Am I figuring this right?  I would then need 75 -100watt system.  How much would that run me?  Am I figuring this right?

BTW I installed these 6 volt batteries this afternoon and they basically work, but I have some questions.  I asjed the shop that sold them to me if they were already charged and was assured that they were.  And yet, when I checked them, they were only at 37% charge level.  Is that typical?  If so how can a dealer store them for any period of time with <50% charge and not suffer degradation?


I ran my genset for a couple of hours and the level meter I have on this read 97% butit  soon settled back to 45%. I know that it takes more than a couple of hours to charge batteries.  I also measured them with a hydrometer and they showed a level of just between fair and good, no doubt due to the lack of full charge


Let me add that I very much appreciate the time that so many have spent to answer my questions on batteries.  I have learned a great deal.  It was good to go back and read that library article on batteries.  While i had read this last year, not all of it was retained..

 

[Larry N.]

I now have two 6 volt Deka batteries that are each labeled :75Amp rating 120 min.  I would assume that this means they could together deliver 75W for 240 minutes when in optimum condition.

When the 6V batteries are used in series as a 12V battery, you don't double the amp ratings -- the doubling took place as a voltage. If you also doubled the amps then you'd be getting four times the power, so if your specs are right then the pair in series will deliver 75 amps for 120 minutes at 12VDC. Often a more useful rating is the amp hour (AH) rating at a 20 hour rate. I don't know which Deka you have but the Deka 8AGC2 Battery is rated:
* 6 Volts
* Amp Hours (20 hr. rate) : 190
* Minutes @ 75 Amps: 110 mins.
* Minutes @ 25 Amps 430 mins.

So a pair of them would deliver:
* 12 Volts
* Amp Hours (20 hr. rate) : 190
* Minutes @ 75 Amps: 110 mins.
* Minutes @ 25 Amps 430 mins.

Hope that helps.

 

[solarman]

Thanks Solarman for your reply.  I now have two 6 volt Deka batteries that are each labeled :75Amp rating 120 min.  I would assume that this means they could together deliver 75W for 240 minutes when in optimum condition.  In your nomenclaturee it would seem to me that these are 150 amp hr batteries, and together these to could deliver 300 amp hours. 1% would be 3 amps and 2% 6 amps. 6 amps at 12 volts would mean 72 watts.  Am I figuring this right?  I would then need 75 -100watt system.  How much would that run me?  Am I figuring this right?

BTW I installed these 6 volt batteries this afternoon and they basically work, but I have some questions.  I asjed the shop that sold them to me if they were already charged and was assured that they were.  And yet, when I checked them, they were only at 37% charge level.  Is that typical?  If so how can a dealer store them for any period of time with <50% charge and not suffer degradation?


I ran my genset for a couple of hours and the level meter I have on this read 97% butit  soon settled back to 45%. I know that it takes more than a couple of hours to charge batteries.  I also measured them with a hydrometer and they showed a level of just between fair and good, no doubt due to the lack of full charge


Let me add that I very much appreciate the time that so many have spent to answer my questions on batteries.  I have learned a great deal.  It was good to go back and read that library article on batteries.  While i had read this last year, not all of it was retained..

For capacity it is normal to specify the 20 hour rate, Larry has posted a table of capacity vs discharge rate.

GC2's are nominally 200 to 230 Ah @ 20 hr rate depending on manufacturer.

you are confusing Amps and Watts.. 

for SERIES connection, VOLTAGE is the sum of all battery voltages and AMP Hours is that of one battery
for PARALLEL connection, VOLTAGE is of one battery and AMP Hours are the sum of all batteries

so for your 6 Volt batteries we have 6 Volts and 200 Ah, therefore in series you have 12 Volts and 200 Ah.

1% of 200 Ah is 2 Amps. for maintenance purposes I would suggest a 50 Watt panel.

Batteries when new may be stored for quite some time on the shelf in an inactive state.
the manufacturer fills the battery with acid of the correct SG so it's effectively fully charged.
as no charging current has been applied, the "destructive" chemical reactions have not yet taken place
and will not effect the life for at least 6 or 8 months.

A new "off the shelf" battery should be fully charged and also given and equalization charge before use ( ideally ).
also, don't expect the battery to give full capacity right away, it usually takes at least 10 cycles before the capacity
comes up to spec..

Note that i'm assuming you have wet cells, if your batteries are AGM then do NOT apply an equalizing charge.

 

[JoelP]

For capacity it is normal to specify the 20 hour rate, Larry has posted a table of capacity vs discharge rate.

GC2's are nominally 200 to 230 Ah @ 20 hr rate depending on manufacturer.

you are confusing Amps and Watts.. 

for SERIES connection, VOLTAGE is the sum of all battery voltages and AMP Hours is that of one battery
for PARALLEL connection, VOLTAGE is of one battery and AMP Hours are the sum of all batteries

so for your 6 Volt batteries we have 6 Volts and 200 Ah, therefore in series you have 12 Volts and 200 Ah.

1% of 200 Ah is 2 Amps. for maintenance purposes I would suggest a 50 Watt panel...

Hi Solarman,

Thanks for your patient replies.  Yes, I mistyped watts when I meant amps.  Still I have a question:

These 6V batteries are labeled as 75 amps for 120 min. With two in series they deliver 12V.  That should mean that they are rated to deliver @ 12V 75 Amps for 2 hours or 150 amp hours, with 1% being 1.5Amp. Right? So then scaling the numbers from your 200 AH needs 50 watt assumption, wouldn't 40 watts of solar do the job for 150 AH? ( Not sure how you went from 2 amps to recommend 50 watts.  W =E x  I  or W = 12V  x 2A = 24W...no???)


Thanks also for explaining the storage and the advise to look for multiple cycles before getting fully charged and conditioned.

 

[solarman]

Hi Solarman,

Thanks for your patient replies.  Yes, I mistyped watts when I meant amps.  Still I have a question:

These 6V batteries are labeled as 75 amps for 120 min. With two in series they deliver 12V.  That should mean that they are rated to deliver @ 12V 75 Amps for 2 hours or 150 amp hours, with 1% being 1.5Amp. Right? So then scaling the numbers from your 200 AH needs 50 watt assumption, wouldn't 40 watts of solar do the job for 150 AH? ( Not sure how you went from 2 amps to recommend 50 watts.  W =E x  I  or W = 12V  x 2A = 24W...no???)


Thanks also for explaining the storage and the advise to look for multiple cycles before getting fully charged and conditioned.

They will provide 75 Amps at 12 Volts for 120 minutes ( if you're lucky ! )

1% of 200 Ah is 2 Amps, 12 V * 2 A = 24 Watts, you need twice this many watts for the panel, so 48 W, rounded to 50 W
always round up..

 

[over40pirate]

True Gary, it's more of an industry reference value that is used for comparison purposes, as you reach lower values of DOD, the electrolyte has more chance of breakdown and therefore reduced lifespan. if you discharge to 100% DOD regularly you will end up with a useless battery real quick..

Edgar Beyn (author of !2 Volt Dr.) told me years ago, when sailing (same 12 volt problems) that draining a battery to zero, knocks off 10% of it's life.