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Thread: Installing a higher capacity deep cycle battery

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    Administrator Daox's Avatar
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    Installing a higher capacity deep cycle battery

    Swarthy got a new battery last night.

    I did not replace it with the standard starting battery, but rather a group 24 deep cycle battery. These are also called marine batteries (but not dual purpose). They are designed to be discharged and recharged where a starting battery isn't. They will die a quick death if you deeply discharge and recharge them. However, the deep cycle does not provide as many cranking amps as a starting battery. I've used deep cycle batteries on several cars and starting has never been an issue.

    Why might you want to do this? It is possible a deep cycle battery may be a bit cheaper than a starting battery. Or, you may be installing a beefy audio / entertainment system and need some additional reserve capacity. Or, you may run a 110V power inverter off your battery and would like some more run time on it. In my case, I plan to disable my alternator eventually. This reduces an accessory load on the engine. This does two things for us. First, it frees up some power that the alternator would otherwise be consuming. And, by freeing up that power, it also means I'll get better fuel economy since I'm not having to use power to recharge the battery.

    You might say "But Daox, your battery needs to be recharged." I agree, and I plan on adding an onboard battery charger and plug in when I am home. This essentially makes my Mirage a mini plugin hybrid! However, that mod info is for another day when I get to it. This is simply the first step toward that. So, lets get back to the battery mod.

    The new battery is slightly larger than the OE battery. Its just about the same height (a little taller), the same width, and a bit longer by an inch or so.





    It fits into the car pretty nice. It is at the extreme of having enough threads on the hold down brackets, but it does work. However, there is a problem where it won't just drop in. The positive and negative terminals are on opposite sides as the OEM battery. There is no way the OEM post connectors have enough slack to make things work, so I had to get some parts to make things work. I got some extension cables. One end of the cable has a female automotive post connector and the other has a flat connector with a hole in it. So, with the flat connector I got a male automotive post with a bolt through it so they can bolt together effectively making an extension cable.







    With the extension cables put together, I was able to install the battery in the car and even hook it up properly. I used a couple zip ties to keep it somewhat tidy. I'll probably clean it up a bit more when its not hovering near 0F outside.




    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing
    Current project: Developing a rear sway bar alternative

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        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 41.7 mpg (US) ... 17.7 km/L ... 5.6 L/100 km ... 50.0 mpg (Imp)


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    Member daleWV's Avatar
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    I don't think I would run a deep cycle battery in a car. They are made for a constant low rate of discharge AND charge. The high discharge of starting and the high rate of charge from the alternator immediately after starting will shorten the life of the battery. Also I wouldn't advise the idea of running without your alternator in service. Your lights (mainly headlights) are going to be quite a bit dimmer for one thing. The accessories in the car that are made to run at fully charged battery voltage will suffer and may operate erratically or slow (radiator fans, heater/AC fan, door locks, window lifts, ABS braking system, etc.). Not sure it would be worth the potential trouble of disabling the alternator. JMHO

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    Eggman (01-05-2018)

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    Moderator Eggman's Avatar
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    Quote Originally Posted by daleWV View Post
    Not sure it would be worth the potential trouble of disabling the alternator. JMHO
    But it sure is interesting to watch someone else try hahahaha.



    By the way I kinda had to do just this for a while on my Colt Estate wagon - but not to save gas. Fun times.
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    Administrator Daox's Avatar
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    Quote Originally Posted by daleWV View Post
    I don't think I would run a deep cycle battery in a car. They are made for a constant low rate of discharge AND charge. The high discharge of starting and the high rate of charge from the alternator immediately after starting will shorten the life of the battery. Also I wouldn't advise the idea of running without your alternator in service. Your lights (mainly headlights) are going to be quite a bit dimmer for one thing. The accessories in the car that are made to run at fully charged battery voltage will suffer and may operate erratically or slow (radiator fans, heater/AC fan, door locks, window lifts, ABS braking system, etc.). Not sure it would be worth the potential trouble of disabling the alternator. JMHO
    I agree with most of what you posted. There are trade offs for doing this mod for sure. Dimmer headlights is one of those trade offs. The rest is really not noticeable in my experience. I have done this on a few other cars now and the headlight brightness is the biggest draw back. I've never had a problem with the other electronics though someone always mentions this as a possible issue (and to be fair, it is). I've always wanted to install a dc-dc boost converter to bump the voltage back up for the lights, but I never have. I doubt I will this time, but we'll see.

    On the other hand, the benefit is quite large though in the MPG department. MetroMPG tested this modification on his 1.0L Metro and saw a gain of just over 10%. The fuel economy benefit is pretty huge for a single modification.





    I have not seen tests done on how much power deleting the alternator frees up, but that would vary greatly from car to car based off how much electrical power the car uses. My estimate would be roughly 2X the power usage of the car. So, if your car uses 20A while in operation, the car is using ~13.5V * 20A = 270W. 270W * 2 (efficiency of the alternator is around 50%) = 540W. 540W is equivalent to around 3/4 horsepower.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing
    Current project: Developing a rear sway bar alternative

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 41.7 mpg (US) ... 17.7 km/L ... 5.6 L/100 km ... 50.0 mpg (Imp)


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    Uber Mirage alex16's Avatar
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    A toggle switch to disable the electric power steering would work great along side of this. It would also be neat to have a switch to disable the alternator as well temporarily for scenarios like climbing hills or entering interstates.
    2014 ES F5MBD aka 5MT. I am a full time Uber driver, if you want to drive for uber DO not sign up without my referral code for a bonus .

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        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 44.8 mpg (US) ... 19.1 km/L ... 5.2 L/100 km ... 53.9 mpg (Imp)


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    Senior Member IchabodCrane's Avatar
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    There are requirements regarding brightness/power of DRLs and headlights so modifications that reduce these values might be illegal and/or make you liable in an accident. So....
    Would there be any possibility of running an electric on/off clutch on the alternator like as on the air conditioning pump? This would allow for Max efficiency during daylight with switchability to full power when headlights are required.

    Ultimately it's not feasible for me as the electrical load in cold climates (where I live) would likely exceed the abilities of the battery on it's own too quickly to realise substantial returns in economy.
    Also the exhorbitant cost of electricity in rural Ontario diminishes any gain in gas mileage as it's almost as cheap to drive the car as plug it in.

    In warmer climes with the bugs worked out it may save a good chunk of change for those who try it though.
    Good luck.
    Will weld for beer.

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        click to view fuel log View my fuel log 2014 Mirage SE 1.2 automatic: 45.3 mpg (US) ... 19.3 km/L ... 5.2 L/100 km ... 54.5 mpg (Imp)


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    Moderator Eggman's Avatar
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    Disconnecting is not necessary. Load is controlled by controlling the alternator field.

    Blue Sea Systems: Alternator Field Disconnect
    Welcome to MirageForum.com
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    And don't forget pictures.
    Mitsubishi Is Not Dead Yet
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        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.5 mpg (US) ... 21.0 km/L ... 4.8 L/100 km ... 59.4 mpg (Imp)


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    Daox (01-07-2018)

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    Senior Member Alex1a1f's Avatar
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    Quote Originally Posted by Eggman View Post
    Disconnecting is not necessary. Load is controlled by controlling the alternator field.

    Blue Sea Systems: Alternator Field Disconnect
    Exactly. Most don't realize that the alternator can be spinning with no power/load/drag being produced.


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    Daox (01-07-2018)

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