Deep-cycle to replace your car battery? An idea.

[Boyntonstu]

A deep-cycle battery is a lead-acid battery designed to be regularly deeply discharged using most of its capacity. In contrast, starter batteries (e.g. most automotive batteries) are designed to deliver short, high-current bursts for cranking the engine, thus frequently discharging only a small part of their capacity. While a deep-cycle battery can be used as a starting battery, the lower "cranking current" implies that an oversized battery may be required.

A deep-cycle battery is designed to discharge between 45% and 75% of its capacity, depending on the manufacturer and the construction of the battery. Although these batteries can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 45% discharge.

There may be a deep-cycle battery that is the exact size replacement for your existing battery.

If you have a deep-cycle house battery and place it in parallel with your starting battery, the pair will become that "oversized battery"  needed to start your car.

At the 50% discharge limit, you should be in great shape to power your house and start your vehicle.

 

[Trebor English]

I have been doing this.  It works.  With a regular small starter battery you need to limit your use severely, to not reduce the life of the battery.  I now have a "75" amp hour group size 24 "deep cycle" battery.  

With golf cart batteries the usual recommendation is to use only 50% of the capacity.  My recommendation for marine trolling motor batteries is a third, 33%.  For car starter bateries, more than 10% regular use will lead to early death, under 5% isn't particularly harmful.  Since they don't have an amp hour rating, calculate it from from the RC rating.  

My battery was 75 ah when new.  A third is 25 ah.  Today the actual capacity is less.  I avoid taking more than 20 ah.  

Don't forget to add water.  Marine and trolling motor batteries are not maintenance free.  Even if their deep cycle characteristics aren't up to golf cart battery standards they still need maintenance like real deep cycle batteries.  My battery uses 20 to 30 ml per cell per month.  Without maintenance battery life would not exceed 3 or 4 months.

 

[Boyntonstu]

I have been doing this.  It works.  With a regular small starter battery you need to limit your use severely, to not reduce the life of the battery.  I now have a "75" amp hour group size 24 "deep cycle" battery.  

With golf cart batteries the usual recommendation is to use only 50% of the capacity.  My recommendation for marine trolling motor batteries is a third, 33%.  For car starter bateries, more than 10% regular use will lead to early death, under 5% isn't particularly harmful.  Since they don't have an amp hour rating, calculate it from from the RC rating.  

My battery was 75 ah when new.  A third is 25 ah.  Today the actual capacity is less.  I avoid taking more than 20 ah.  

Don't forget to add water.  Marine and trolling motor batteries are not maintenance free.  Even if their deep cycle characteristics aren't up to golf cart battery standards they still need maintenance like real deep cycle batteries.  My battery uses 20 to 30 ml per cell per month.  Without maintenance battery life would not exceed 3 or 4 months.

Do you have house batteries in parallel?

Like this one?  https://www.westmarine.com/buy/west...arine-battery-75-amp-hours-group-24--15020316

 

[Trebor English]

If you have a deep-cycle house battery and place it in parallel with your starting battery

Do not connect different lead acid batteries in parallel without a disconnect switch.  Only connect them together when there is a charge source or when there is a heavy load that requires both.  

The maintenance free starter battery has calcium in the plates.  The deep cycle house battery does not.  The acid concentration when the batteries were made was different.  Their temperatures are different.

 

[Trebor English]

Do you have house batteries in parallel?

No.  I have one battery in the original location, under the hood.

 

[Boyntonstu]

No.  I have one battery in the original location, under the hood.

I meant placing them in parallel if using the same chemistry in all locations.

I some of my older cars there was sufficient space to place a larger groups size instead of the OEM battery.

I always went to a larger size if possible.

 

[John61CT]

If the batts comprising a bank are separated by any distance, getting the very heavy gauge wiring into a balanced scheme is the big challenge.

Not so critical if only combined for charging, but then you lose the Peukert advantage of size.

 

[Gideon33w]

In my first van I used a common battery for starting and house. Just went plenty oversized.
Still isn't the best setup. The high load for starting is rough on even a large deep cell.
And you shouldn't parallel a deep cell and a house battery. Batteries need to be the same.
Adding distance between batteries is the same as adding distance to any DC system. Bad.
At the end of the day, it's all disadvantage and no advantage to pairing systems.

 

[Boyntonstu]

In my first van I used a common battery for starting and house. Just went plenty oversized.
Still isn't the best setup. The high load for starting is rough on even a large deep cell.
And you shouldn't parallel a deep cell and a house battery. Batteries need to be the same.
Adding distance between batteries is the same as adding distance to any DC system. Bad.
At the end of the day, it's all disadvantage and no advantage to pairing systems.

Many cars such as the Cadillac Deville have their batteries located under the back seat.

Distance is not bad if proper wiring is used.

"And you shouldn't parallel a deep cell and a house battery. Batteries need to be the same."

Agree.   Use same chemistry as stated above.

 

[Gideon33w]

I mean the distance between two batteries on the same charge system.
I've ran rear and mid mounted batteries on several track toys without issue.
I just wouldn't want two batteries in parallel with several feet of cable between them.

 

[John61CT]

A few feet with high gauge cable no problem.

20-30 feet gets more problematic with high amp rates.

But **balancing** the wiring gets more complicated, the weakest link syndrome hurts bank longevity.

 

[Boyntonstu]

Please explain "But **balancing** the wiring gets more complicated"

 

[Boyntonstu]

I mean the distance between two batteries on the same charge system.
I've ran rear and mid mounted batteries on several track toys without issue.
I just wouldn't want two batteries in parallel with several feet of cable between them.

Electrical plan - dual batteries >20 feet apart

http://forums.iboats.com/forum/gene...-electrical-plan-dual-batteries-20-feet-apart

and a quote:

[font=Arial, Helvetica, sans-serif][font=Arial, Helvetica, sans-serif]Re: Electrical plan - dual batteries >20 feet apart

I've been doing what you first described for years. I have a 10 gauge wire with a 30amp fuse ON EACH END running from the rear battery to the front battery with a switch that allows me to charge the front battery. ALL accessories are run off the front battery including a 55# minnkota. I've never popped the 30amp fuse even if I forgot the switch on before starting the engine. A fully drained lead acid deep cycle still only accepts about 15-20amps max while charging so 10gauge/30amp is plenty. I've taken a full drained group 27 deep cycle and hooked it to my battery charger which has a 50amp quick charge mode and the amp gauge only shows a 20 amp charge and that's with the charger pushing 15v+ at it so no need to worry about flipping to switch on a dead front battery. If you have an Orbital, Optima, or other fancy deep cycle then I don't know as I don't know how much charging amperage they draw.[/font]
[/font]

 

[Gideon33w]

10 gauge wire ... I stopped reading there ... Don't copy that setup unless you need insurance money ...

 

[user 15722]

This is fascinating for me to read !
Which probably translates, correctly, that I don't want to spend the big bucks to buy and install a proper system According to Hoyle, yet what I do assemble will be for critical machines and it must function well, from day one.
Or I'm off looking for a park with shore power. :-(
So far, purchasing used batteries at a discount price from the local battery store hasn't worked out so well, either.
Mismatched age, condition, and capacity will force me to run multiple systems for different loads within the house.
I suppose it will be the CYA thingy and call it redundant systems. wheels

 

[John61CT]

> Please explain "But **balancing** the wiring gets more complicated"

The canonical howto
http://www.smartgauge.co.uk/batt_con.html

Each intra connect wire same gauge same length.