Single battery system?

[Trebor English]

In a prior thread,
https://vanlivingforum.com/Thread-Portable-Power-Banks
it was suggested that the starting battery be upgraded and also used as a house battery.  My starting battery is nearing the end of its useful life.  I am considering  a deep cycle 27 or 31 to replace it and letting the AGM 70 Ah house battery go to a good home.  The batteries I am considering are probably real deep cycle as they actually have Ah ratings, 90 and 105, not just reserve capacity minutes.

I use very little electricity.  I have no water pump, refrigerator, or TV/DVD.  I charge my cell phone and I use an electric shaver.  That's 2 - 3 Ah per day.   I  use a disconnect switch to turn off all vehicle circuits, lights, computers, door locks, etc. I rarely stay put more than a week.  If I limit discharging to 25% instead of the typical 50% the recharging should be closer to what the alternator/regulator was designed for.  

Has anybody done this?  What are the pitfalls?  What am I missing?

 

[LeeRevell]

Sounds like you are going with a Marine battery, not a true Deep Cycle. I hope so. Deep cycle batteries are NOT designed for the short but intense starting load.
Also a true deep cycle battery won't fit a battery tray under your hood. A bigger Marine Battery may not fit either. Measure the battery and the tray space before buuing.

 

[ccbreder]

While a deep cycle battery can and will start the engine, they are not designed for that service. You would be better served with a "marine" type combination battery to use as starter and occasional deep cycle service. Then keep your house battery as a true deep cycle. That said, you can operate from one battery, using 25% may leave enough to start the engine. Or you drain a bit more and it will not. That is the real problem with one battery.

 

[SternWake]

I currently use 90Ah of AGM for both house and engine, and i use 35 to 55Ah each night, but I have 200 watts of solar. It is a NOrthstar AGM which has very high CCA ratings for engine starting, and deep cycling ability. But it is not Optimized for Deep cycle service like Lifeline AGM

An AH rating versus RC capacity rating does not mean true deep cycle. There are very few true deep cycle flooded/wet 12v batteries.

I'd not bother with a dedicated house battery with your stated loads.

The 100% charge is still required. you will likely be hovering in the 85 to 95% range relying on the alternator. It still takes hours at absorption voltage to reach 100%.

My Northstar AGM requires the high amp recharge from most depleted state, after a few deep cycles and a low and slow solar only recharge to 100%, to return best performance.

Not sure how the lesser$$ AGMS would fare being cycled in the 85 to 95% range. A lot will have to do with the vehicles voltage regulator. These are hardly optimized for best recharging, especially on a deeper cycled battery. How much the lifespan is shortened by less than perfect recharging is an unknown and highly variable

 

[RVTravel]

Laren used a single Walmart deep cycle battery.

https://groups.yahoo.com/neo/groups/VanDwellers/conversations/messages/138990

 

[Optimistic Paranoid]

AFAIK, the comments about marine/rv batteries not being TRUE deep cycle, and so on, are true, but only in reference to the old Flooded Lead Acid batteries.

Modern AGM batteries seem capable of starting engines easily, and still surviving lots of discharge/charge cycles like a true deep cycle.