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Thread: Time to rethink the battery situation

  1. #1
    Still Plays With Cars Loren's Avatar
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    Time to rethink the battery situation

    I've been running a tiny 6-pound battery for about 2 years now. You can read about that here: Lightweight Battery Project.

    The YTZ10S battery that I've been using is about an 8AH battery with 120CCA.

    For reference, the OE battery is a closer to 50AH and 350CCA.

    This little battery has been reliably starting the car for almost 2 years. Well, that's not quite true. The first battery failed due to an OBD2 device drawing current when the car was off. Repeatedly discharging it to nothing didn't do it any favors. So, the current battery went in back in 11/2019. So, it's been about a year for THIS battery, and 2 years of using this size of battery. It does seem a little sluggish starting if I let it set for more than a week, and I have had to jump it once or twice due to that. (COVID has had me in a state of not driving my cars much) The cheap battery that I bought also seems to have a slight leak, and it showing some corrosion on the tie-down bracket. Otherwise, for a $30 battery that weighs almost nothing, I can't complain too much.

    For my purposes, if I were closer to "daily driving" the car, it would be adequate. Bear in mind that I live in Florida where 50 degrees is considered downright frigid.

    But, now I've quit autocrossing the car, so "ultimate light weight for performance" is less of a concern. And I've started getting more into hypermiling the car, and engine-off coasting a lot... and I want to be able to reliably restart the car for many more cycles while I'm driving it. So, I need more battery capacity. I don't think I need a full 34 pounds of OE battery capacity, but more than I have would be nice.

    I think I've settled on a nice YTX30L motorcycle battery. It weighs just under 20 pounds. (14 pounds more than the itty-bitty battery, but still 14 pounds lighter than stock) The price is a low $55. 30AH capacity, 385CCA. Not bad.

    I still might change my mind and go with a bigger, possibly deep-cycle battery. Hypermiling is a harsh mistress.


    Simplify and add lightness.

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    Still Plays With Cars Loren's Avatar
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    I spent a good chunk of time this evening revisiting Daox's "alternator delete" thread.

    I was thinking about possibly implementing it, maybe with a circuit to trigger enabling the alternator only when battery voltage reaches a certain threshold (maybe 11.7ish?), and letting it charge up maybe a half volt more before shutting off again. That will leave me at the end of any given drive with battery voltage somewhere between 11.7 and 12.2. And then, rather than relying on a plug-in charger to replenish the battery at home (I just don't wanna have to plug in my car), do a solar charger aiming for a 1-2A trickle charge. (20W solar panel with a proper charge controller can be had for around $65) That should be able to top it off with 8-10 hours in the sun. (plus, it would even be charging while I was driving... if it was sunny)

    The "brake regen" logic doesn't seem to make much sense when using engine-off coasting. I don't do a lot of braking with the engine running, or at all if I can avoid it! But, if I just have the alternator disabled until a certain low voltage threshold... it should be disabled for most or all of my short trips. And then it will be enabled as-needed. And, I won't have to worry about over-discharging the battery.

    What I don't know (MetroMPG???) is... the reported 5-10% improvement in FE that can come from disabling the alternator... is that IN ADDITION TO hardcore hypermiling as I'm already doing? How much improvement should I expect to see over my current significant EOC hypermiling numbers? In other words... is it even worth it?
    Simplify and add lightness.

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    Senior Member dspace9's Avatar
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    Quote Originally Posted by Loren View Post
    hypermiling numbers? In other words... is it even worth it?
    I still have my original battery in my Mirage. I should get a new one. I actually had planned on getting one when mine went kaput through CAA. Happened to be my Mirage wouldn't start one morning about 6 months ago; I call road side assistance, and turns out they don't do battery changes in my location. All because I am rural and have a PO BOX. They didn't say that, but really "my location" excuse says it all. I should be able to get battery replacement service.

    Well how ironic is that? The sort of person who would need the service in the boonies can't get it. Don't know why I pay for roadside assistance. What if my car breaks down and I am lost? That was the whole point of having CAA. So I might cancel my membership, but my list of essential things to cancel is too much for me to remember.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 42.2 mpg (US) ... 17.9 km/L ... 5.6 L/100 km ... 50.7 mpg (Imp)


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    Quote Originally Posted by Loren View Post
    What I don't know (MetroMPG???) is... the reported 5-10% improvement in FE that can come from disabling the alternator... is that IN ADDITION TO hardcore hypermiling as I'm already doing? How much improvement should I expect to see over my current significant EOC hypermiling numbers? In other words... is it even worth it?
    You can do some estimates. According to Wikipedia the amount of energy in petrol is about 33*109J/m3 which is 33*106J/l, which is 33MJ/l. A typical engine has a return of 25%, so you get around 8.5MJ/l.
    When running 50mpg, which is 21.26km/l, you use 0.4MJ/km. At 60km/h (37.3mph) you use 0.4MJ/60sec = 6.7kJ/sec = 6.7kW.
    Crosscheck, the engine can deliver ~75hp which is 55.9kW. So 6.7kW is a reasonable value.
    AFAIK a typical alternator has a return of 50%, so to get 5% better mpg you should use (6.7kW/20)/2 = 167W less electricity. That doesn't sound unreasonable, if your car actually draws that much.
    On the other hand, 167W is 13.9A@12V. So your 30Ah battery will drain in 2 hours, if you kill the alternator. Assuming you can never use break energy to charge the battery. (Which cannot be much anyway, I don't think the alternator can deliver more then few dozen A, and breaking doesn't last long).

    If the car is taking 167W, it might be more easy to save on that. How about disabling power steering?

        __________________________________________

        click to view fuel log View my fuel log 2013 Space Star Cleartec Intense 1.0 manual: 55.7 mpg (US) ... 23.7 km/L ... 4.2 L/100 km ... 66.9 mpg (Imp)


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    Senior Member fc321's Avatar
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    I actually went in the completely other direction than you buy purchasing a $49 battery at Walmart that is actually Larger than the stock battery:

    https://mirageforum.com/forum/showth...attery-(Large)

    It has worked splendidly since Install, and I think it is the cheapest value because it has more CCA than the Mirage requires and therefore it should last a year or 2 extra than the stock one because as the battery degrades it still has a higher capacity so even at 65% lifespan it should still be working fine
    2015 Mirage DE 5 speed Manual - 30k miles

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 44.9 mpg (US) ... 19.1 km/L ... 5.2 L/100 km ... 53.9 mpg (Imp)


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    Quote Originally Posted by dspace9 View Post
    I still have my original battery in my Mirage. I should get a new one. I actually had planned on getting one when mine went kaput through CAA. Happened to be my Mirage wouldn't start one morning about 6 months ago; I call road side assistance, and turns out they don't do battery changes in my location. All because I am rural and have a PO BOX. They didn't say that, but really "my location" excuse says it all. I should be able to get battery replacement service.

    Well how ironic is that? The sort of person who would need the service in the boonies can't get it. Don't know why I pay for roadside assistance. What if my car breaks down and I am lost? That was the whole point of having CAA. So I might cancel my membership, but my list of essential things to cancel is too much for me to remember.
    If you still have a 2014 factory battery that has survived several Canadian winters, your factory battery has done quite well. Since a factory battery only has 356 CCA, it doesn't take much to turn these cars over. Higher CCA doesn't guarantee longer batter life, but most aftermarket batteries will have more.

    Replacing tires & batteries comes with car ownership. Not a big deal in my mind.

  9. #7
    Senior Member dspace9's Avatar
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    Quote Originally Posted by Mark View Post
    If you still have a 2014 factory battery that has survived several Canadian winters, your factory battery has done quite well. Since a factory battery only has 356 CCA, it doesn't take much to turn these cars over. Higher CCA doesn't guarantee longer batter life, but most aftermarket batteries will have more.

    Replacing tires & batteries comes with car ownership. Not a big deal in my mind.
    My battery has done quite well. I have weird hours at work so I start my Mirage at 2 AM in the middle of winter, and it gets going. I'm wondering how much longer my front lights are going to last as well. Like you say Mark it's all part of owning a car. I got new plates not long ago.

    CAA is good to have because once my old Ford Escort broke down in the UP Michigan.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 42.2 mpg (US) ... 17.9 km/L ... 5.6 L/100 km ... 50.7 mpg (Imp)


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    Quote Originally Posted by dspace9 View Post
    My battery has done quite well. I have weird hours at work so I start my Mirage at 2 AM in the middle of winter, and it gets going. I'm wondering how much longer my front lights are going to last as well. Like you say Mark it's all part of owning a car. I got new plates not long ago.

    CAA is good to have because once my old Ford Escort broke down in the UP Michigan.
    I have spare headlights & jumper cables stored in my car. My battery has been good so far, but I have a 2017.

    I am visiting my parents in NE Wisconsin at the moment. I am only 15 miles from the UP.

  11. #9
    Senior Member dspace9's Avatar
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    I haven't been to the UP since 2014. But I started visiting there when I was a kid. I drove my Mirage up there about 3 months after buying my car brand new. Still holds the record for fuel economy logged on my trip computer: 4.2 L/100 km's on the bridge.

    I have relatives with a cottage in the UP right on Lake Michigan. I think they sold it now. Not too sure what happened with that. Lots of memories.


        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 42.2 mpg (US) ... 17.9 km/L ... 5.6 L/100 km ... 50.7 mpg (Imp)


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