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Testing health of Coach batteries without a load bank

October 25, 2020, 10:39:49 pm

To all of you electrical gurus out there, with special note to Roger.

My 3 coach batteries MK SG8D are still the original ones, so 17 years old.

I am contemplating  replacing them before I make a longer trip in early spring.

But I am curious to find out in what shape they presently are in.

I do not have a load bank and do not know anybody around here that has one. I Have disconnect the coach from shore power today at noon , left the domestic refrigerator and aquahot heating on 110 v on (outside temperature was about 20 deg F) and recorded the following.

Time 12:00 hrs    Battery V 14.1 V  LR Temp 62 F  BR Temp 52  Inverter AmpHr      0
Time  02:00 hrs                    12.4                    67                    53                              -28.8
Time  05:00 hrs                    12.4V                58                    56                              -63.1

It was getting dark and  colder outside I switched back to shore power.

Question:

Can one make an estimate from these limited data towards the health of the batteries?
If not, for how long do I let the batteries drawn down?

I read the report in the archive of Roger replacing his 8D AGMs with LiFeP04 batteries.

It is apparent that the LifeP04 batteries are the technically superior selection with more reserve capacity.

Is the following an accurate summary?

QTY 3 Lifeline SG8D              with 5 year Warranty        $ 750 ea    150 lbs ea
QTY  4 LiFeP04 100Amp            10  year warranty          $ 900 ea    31  lbs ea

Answers are greatly appreciated.

Regards

Klaus

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Re: Testing health of Coach batteries without a load bank

Reply #1 – October 25, 2020, 11:23:52 pm

When you take your batteries off the charger they will at a higher voltage because of the charger.  With some load for a while and then the load removed they will be at about 12.7-12.8 v, fully charged assuming they have been on the charger for a couple days.  Disconnect charger, turn on your inverter, add a 100 - 150 watt load.  That (along with the inverters load and efficiency) should put about 13 amp load on the battery.  Check the battery voltage once an hour or so until you get to 12.1 volt. Remove the load, turn off the inverter.  Measure the voltage again. with no load it will go back to about 12.2 volts.  At this point you have used 50% of your capacity. 

For example, If it takes 24 hrs that will be 24x13=312 amp hrs.  If that is 50% then your battery set is good for 312x2=624 amp hrs.  Your batteries were probably good for about 720 amp hrs total when new.  That is about 13% loss.

Lifeline AGMs are a high end choice. 
Full River makes L16 sized 6V AGM batteries, 4 get you 830 amp hrs and fit in the space pf two 8Ds.
O'Reilly's are a good budget choice. 
Long ago GELs might have had some advantages relative to AGMs but not so much anymore.

BattleBorn's are a great choice too.  With an LP refrig 4 will do fine and save a bunch of weight. If you charge at 20% of capacity or less and use 50% of your capacity each day you should get 20 years out of them or more.  6 batteries gets you more reserve, less daily % of use and even longer life.  and they have a 10 yr warranty.

LiFePO4 batteries have limitations at +125 degrees F.  Are you camping in Death Valley in the heat of the summer?  And there is no practical low temp limit for batteries in use. It is not the ambient outside temperature but the temperature inside of the battery. Cold limits apply to charge rates on batteries at rest in cold temperatures.  Once the battery is warmed up by use or other means (such as running the AH in the basement) it operated normally.

These are choices driven by how you want to use your coach, what your expectations are, what your budget is, can you do the work yourself and how long you expect yo keep your coach.

It is worth learning all you can and figuring out the best solution for you.

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Re: Testing health of Coach batteries without a load bank

Reply #2 – October 26, 2020, 09:57:02 am

Klaus,

I am in the process of changing out to a Lifepo4 system with 400ah for about the same amount as you are quoting for 100. Now this isn't a Battle Born system so check around for pricing. I would have went with the BB but found a system that better suits our needs.  The weight of battery to ah rating is a win win.  If you are in need for battery replacement then lifepo4 is a good option. 

Mike

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Re: Testing health of Coach batteries without a load bank

Reply #3 – October 26, 2020, 11:58:51 am

Mike,

Please send me the spec and source for the 400 Amp battery.
How many are you putting in?

Regards

Klaus

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Re: Testing health of Coach batteries without a load bank

Reply #4 – October 26, 2020, 12:39:49 pm

Klaus,

Check your P/M

Mike

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Re: Testing health of Coach batteries without a load bank

Reply #5 – October 26, 2020, 06:28:51 pm

 I started this post, and I know now much more about batteries than I did before.
(I actually new nothing about LiFe deep cycle batteries, which strike me as a very interesting product.)
I greatly appreciated the inputs I received.

In my former working life one of my standing instructions to my engineers was " I do not tolerate Email wars on any subject, that is unprofessional "

 Regards

Klaus

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Re: Testing health of Coach batteries without a load bank

Reply #6 – October 26, 2020, 09:42:44 pm

Sic tacuisses, philosophus mansisses.

Regards

Klaus

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Re: Testing health of Coach batteries without a load bank

Reply #7 – October 27, 2020, 06:38:20 am

Klaus,

Very well stated.

Mike

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Re: Testing health of Coach batteries without a load bank

Reply #8 – October 28, 2020, 08:29:00 pm

MULTIPLE erroneous and nonsensical posts have been removed from this topic and the poster has been put on moderation.

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