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Thread: Why does my 3year old Optima rest at 12.5 volts

  1. #1
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    Why does my 3year old Optima rest at 12.5 volts

    I have a 3year old Optima blue top light grey box ie dual purpose battery in my 2002 D2 TD5 auto.

    I have fitted this to an ARB tray near the turbo with a stainless heat shield between and it is the starting battery. My second battery is now a130AH AGM battery fitted in the original position and now controlled by a simple ign triggered solenoid. This replaced an ABR electronic battery controller which cut off at 12.4 volts. ( the reason for the solenoid is that I intend at some stage to fit a Lithium Battery)

    I bought the Optima in Brisbane from a dealer who informed me it was lucky to last 2 years! This was after I had starting difficulties on a trip North which I later found to be injector seals.

    The conundrum is that the battery never shows a surface charge of say 13.2 volts after being charged but within a few minutes reverts to 12.5 volts if charged with an external charger on float at 13.6 volts , whether connected to the car earths or not. After driving I never see over 13 volts on shutdown. I have a dash switchable meter which shows 12.5 or so immediately. Contrast this to the new AGM which is still showing 13.1 volts after a day's rest. My alternator is starting charge at 14.6-7 depending on temperature dropping to13.9-14.0 when hot. I have checked the dash meter against my multimeter and they agree.

    I have an admittedly cheapo battery tester which claims it still has 665CCA out of the original 760CCA so is rated good.

    Current when tested on the negative terminal is 0.014amps after charging

    When starting it drops to say 11.7volts with pump and capacitors then up to about 12.3-4 or so if I wait for the check lights to go out.

    It has strong starting with the starter going fast and catching immediately.

    My question whether this is a normal trait of an Optima battery . It has no swelling or acid leakage at all and seems in good condition.

    I am a bit disenchanted with Optimas now and have modified my cradle to fit an Exide Gold plus XDIN66HDMF 760CCA which is low enough to fit with correct terminal orientation, and the right length for my modified tray. But I don't want to buy a new battery if I can avoid it.
    Comments welcome
    Regards PhilipA

  2. #2
    DiscoMick Guest
    12.5.is almost fully charged so that's not a problem. Our Defender is similar.
    When your vehicle is parked there may still be a small drain on it from vehicle functions.

    Higher surface charges drop down as soon as the battery is put under a load, as it would be when driving.
    Does it hold 12.5 if you leave it sitting for a few days? If it loses a lot of charge, that may indicate a problem.

  3. #3
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    Does it hold 12.5 if you leave it sitting for a few days? If it loses a lot of charge, that may indicate a problem
    No over a few days it will reduce to say 12.35.

    I measured the drain at 0.014 amps , but this was with the battery unearthed and I guess the ECU asleep . At least it shows that there are no parasitic drains such as a light on. .

    It is possible that my wife's Lithium charger is wakening the ECU I suppose as it is as noisy as hell in the radio.
    But still the voltage should start at say 12.7 and then drop to say 12.4 as that is 75% charged or should be a drain of about 13amps for a 55AH battery. That is more like 4amps drain which should be noticeable.

    Regards PhilipA

  4. #4
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    Quote Originally Posted by DiscoMick View Post
    12.5.is almost fully charged so that's not a problem.
    Nope, 12.5V is more like 75% soc or less and would seem to be a problem if that's what you get after charging.

    This from Optima's website:

    Fully charged, engine not running, starting batteries (all REDTOP® or BLUETOP® 34M) should measure about 12.6 volts to 12.8 volts. Deep-cycle batteries, including all YELLOWTOP® and dual-purpose BLUETOP batteries, should measure approximately 13.0 to13.2 volts.

  5. #5
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    Your battery will not maintain a surface charge with a load connected to it as the 'floating' electrons are soon bled off.

    What happens if you disconnect the battery, charge it at a good 14.5 volts or so with your external charger and then measure the open circuit battery voltage ? I used to run a bank of 4 Optimas in the Oka as a house battery and they would often hold a surface charge of 13+ volts overnight.

    Regarding your battery tester, what battery internal resistance does it show ?, I find this to be a more accurate measure of battery condition than a derived CCA figure. I'd expect less than 4 milliOhms for your battery.

    Deano
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    86 RR 'classic'......99 Range Rover P38a
    94 Defender 110..95 Defender 130 Ute
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    04 D2a Td5..........02 Disco 2 V8

  6. #6
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    Deep-cycle batteries, including all YELLOWTOP® and dual-purpose BLUETOP batteries, should measure approximately 13.0 to13.2 volts.
    Yes well that is what I expect as it is a light grey blue top. The new house battery AGM holds over 13 for at least a day.

    I have attached a Megapulse to it over the last couple of days and I noted today on shutdown it was 12.72volts after its dip to 11.9 or whatever so it may be going up.

    I also bought a Bosch specific AGM battery charger which I attached today and it went onto float at about 13.3 volts within minutes.
    I don't think my tester gives the internal resistance.
    It has still got me stuffed.
    Regards PhilipA

  7. #7
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    You could try amp counting to see how much you still get from the battery.

    I have done this with my gel batteries and although not extremely accurate you should get a good idea. This is what I did:

    Take a simple inverter with voltage cutoff (10.5 volts or thereabouts), take a steady load like an old school incandescent light bulb of some wattage, I used 70watt iirc. You could also use a 12v high power halogen bulb and skip the inverter but you would have to monitor the battery voltage yourself.
    Charge the battery to it's fullest and hook up the inverter with an ammeter in line. Now set a stop watch. When the voltage cutoff of the inverter kicks in mine starts beeping like crazy. I used a gopro in timelapse mode to make things easy so I could read both voltage and amps every minute or so. You should be able to add them all up to see how many amps you have pulled from the battery and I am sure optima has a table describing how much power you should be able to pull from the battery at a certain amount of current.

    Once the battery is drained, recharge it immediately, don't leave it empty!

    if you now take the original capacity of the battery and the amount of amps you could withdraw from the battery with this test you can see how much of the original capacity is still left.

    Cheers,
    -P

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