Chassis Battery---Deep Cycle Battery---Start Engine---HELP?

[MrMudstud]

OK guys, this is my setup. 2-6 volt 280 amp/hr batteries (9 months old) using 2/0 battery cable. 3000 PSW Renogy Inverter. 540 watts solar panels. 1500-watt microwave. I ran 10-gauge wire from the inverter to the rear outside cabinet to connect to the shore power that goes to the transfer switch circuit before the breaker panel. I also installed a switch to disconnect the house charger/converter when on the battery mode.

Question:
1. The last few times I ran my microwave on the batteries, I notice the chassis battery was drained to 10.5 volt before the solenoid at the battery management system disconnected it, meaning it is dead. It is 6 years old and did it’s time. My question is, since it is connected with the management system, what do you experts think if I get a large 12volt deep cycle battery to use as my chassis battery. Yes, I know, it is not intended for a large heavy draw like a CCA battery, but since I have a switch on the dash that connects house batteries to the chassis battery when needed, will that work.

Then when I need a little extra help for the house side, the chassis battery will help. If I kill all 3 batteries, I can use the solar to build enough energy in a couple of hours to start the coach. My V-10 starts really easy, as soon as you turn it on, it starts immediately. So, I wondering if my thinking is a disaster or is very doable.

Thanks in advance for your assistance and help with your information. Y’all have a great day.

[Winterbagoal]

I've used hybrid AGM (deep cycle with some cranking amps) batteries in all of my last 5 or 6 vehicles as starters. They make great starting batteries, and if you need to combine them with your house batteries to help out, it should work. I know of one other RVer that did exactly that, IIRC, he had control over when the various battery banks (he had 3 I think, 2 separate coach pairs, and an AGM starter) were separated and combined, by manual switches.

[Mr_D]

Originally Posted by MrMudstud

OK guys, this is my setup. 2-6 volt 280 amp/hr batteries (9 months old) using 2/0 battery cable. 3000 PSW Renogy Inverter. 540 watts solar panels. 1500-watt microwave. I ran 10-gauge wire from the inverter to the rear outside cabinet to connect to the shore power that goes to the transfer switch circuit before the breaker panel. I also installed a switch to disconnect the house charger/converter when on the battery mode.

Question:
1. The last few times I ran my microwave on the batteries, I notice the chassis battery was drained to 10.5 volt before the solenoid at the battery management system disconnected it, meaning it is dead. It is 6 years old and did it’s time. My question is, since it is connected with the management system, what do you experts think if I get a large 12volt deep cycle battery to use as my chassis battery. Yes, I know, it is not intended for a large heavy draw like a CCA battery, but since I have a switch on the dash that connects house batteries to the chassis battery when needed, will that work.

Then when I need a little extra help for the house side, the chassis battery will help. If I kill all 3 batteries, I can use the solar to build enough energy in a couple of hours to start the coach. My V-10 starts really easy, as soon as you turn it on, it starts immediately. So, I wondering if my thinking is a disaster or is very doable.

Thanks in advance for your assistance and help with your information. Y’all have a great day.

You only have 140 amp hours of usable battery with your setup. Two 6 volts in series give you 12 volts with 140 amp hrs till 50% drained.
My rig has 4 - 8D 255 amp hr 12 volt Lifeline batteries for the house and 4 - 925 CCA 12 volt starting batteries and 400 watts solar.

[twinboat]

Yes you can use deep cycle batteries as starter batteries.

They don't have the CCAs of a starter battery but they can still deliver enough CAs.

[Old Scout]

Sorry, but I am a bit confused here:
1- two 6-volt house bats aren't much power, a 3000watt inverter could drain them quickly.
2- Microwaves are a huge draw--warm a cup of coffee or a sandwich. [30-40 sec].
3- usually you keep the chassis bat[s] at full status to start rig's engine.
4- manage your power needs with your house bats--panels, genset, shore power.
5- use your boost button to help chassis bat start engine; not the other way.
6- that said--inverter should never be able to drain your chassis bat.

Bottom-line is you don't have a lot battery power do much besides lights, some computer time and a bit of TV--IMHO.

[Mark_K5LXP]

Originally Posted by Mr_D

You only have 140 amp hours of usable battery with your setup.

Why aren't the other 140Ah usable?

Mark B.
Albuquerque, NM

[Mr_D]

Originally Posted by Mark_K5LXP

Why aren't the other 140Ah usable?

Mark B.
Albuquerque, NM

With a lead/acid battery you don't want to go below 50% SOC. So 12.2 or 12.1 is as low as you want to go. Lower and it drastically shortens the battery life.
Now, if you have Lion batteries it's a very different story.

[twinboat]

Originally Posted by Mr_D

With a lead/acid battery you don't want to go below 50% SOC. So 12.2 or 12.1 is as low as you want to go. Lower and it drastically shortens the battery life.
Now, if you have Lion batteries it's a very different story.

If you discharge your battery down to 15% to 20% charge, every time you use it, you cut the total cycles in half. That's every time you discharge them !

500 near full discharges compared to 1000 50% discharges.

Is that drastic ?

Lithium batteries are the same. The more you use each cycle, the less cycles you get.

[ByeTheWay]

All I have is deep cycle. Starting and House all hooked together in Series/Parallel.

[Winemaker2]

Originally Posted by Mr_D

With a lead/acid battery you don't want to go below 50% SOC. So 12.2 or 12.1 is as low as you want to go. Lower and it drastically shortens the battery life.
Now, if you have Lion batteries it's a very different story.

Above is an often repeated myth and many keep repeating it so others believe it.
See twinboats response for the correct answer!

Look at other points on the life cycle chart as well and you will find that you get roughly the same amp hours out of a battery no matter what SOC /DOD you run them to (as long as you don't get too close to 0% SOC or 100% DOD)

25% DOD = 2000 CYCLES
50% DOD = 1000 CYCLES twice the AH half as many cycles as the top case
Both deliver the same AH over their life!

[Yosemite77]

[ATTACH]
I thought I’d rotate this to make it easier to read

[Smitty77]

Originally Posted by Winemaker2

Above is an often repeated myth and many keep repeating it so others believe it.
See twinboats response for the correct answer!

Look at other points on the life cycle chart as well and you will find that you get roughly the same amp hours out of a battery no matter what SOC /DOD you run them to (as long as you don't get too close to 0% SOC or 100% DOD)

25% DOD = 2000 CYCLES
50% DOD = 1000 CYCLES twice the AH half as many cycles as the top case
Both deliver the same AH over their life!

Don - I get what your trying emphasize here... But I believe Mr D's comment is ' a myth'... I think at a 'high level', and under the context that Mr D was responding to - 50% SOC bottom for non Lithium is a valid good statement on 'balancing power usage to battery life'. And I think Twinboat's response and chart info reinforces that?

NOT A BIG DEAL! But for so many coach owner's I meet and talk with along our travels, and on forums too - for Wet and AGM batteries, I feel a goal of living on the top 50% of the battery bank, is appropriate.

What I do feel is missing on many coaches, is the SOC reporting capability. Voltage reading seems to be the norm for way to many RV's. And that is dangerous, if not fully understood. (And hey. I know you, Mr D, Twinboat and many other's know this... But many people read these forums for info, and the devil is in the details. THUS, why I responded, and add my thoughts!)

For those with only 'Voltage Level Indicator's'... Understanding the difference between 'Under Load' vs 'Resting' voltage levels is important. (And not to go too far down this path. I'll add for 'Under Load', the 'Average AH Draw' is an important element too.).

I always encourage those with only Voltage Level Indicator's, to contact their specific Battery Manufacture's Tech Support, and ask for Under Load Voltage to SOC values. And if possible, provide the Battery Manufacturer with our 24 hour Average Amp Hours usage. (When in doubt, suggest asking for 15-20A Average Amp Hours usage, for combo Propane (Refrigerator/Stove/Oven) coaches. And 20-25A Average Amp Hours usage for All Electric coaches/RV's. (Best to actually spend the funds for a Shunt and SOC meter!).

OK, done adding this follow-on $.02... I do feel that without good usage info, and for Wet/AGM batteries - the best practice is as Mr D suggested - live on the top 50% of your battery bank. (And sure, occasional dips down lower will not 'kill a battery. Heck, probably more battery banks have shorter lives from not being fully recharged at least every 4-6 days, the from those who sometimes draw down to say 30% SOC from time to time!)

Best to you, and all,
Smitty