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Thread: Twin boot batteries in parallel

  1. #1
    What search button? Club Member Delboy52's Avatar
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    Twin boot batteries in parallel

    Recently I had a battery die on me by making the house stink of eggs (garage is integrated into the house). It had heated up, warped like a muffin and popped a cap.




    I thought this might have been due to me trickle charging it on a constant low voltage, but the settings on my Ctek charger were set to option 3 AGM which charges the battery less frequently but at a higher voltage. This is to lessen pronlonged heat build up from charging which these types of batteries have got issue with.

    So I replaced that battery with something even better, two of the same type! They are small and fit very discreetly in the sub well behind the seat. I have two as the previous one would be running out of power in a week if not charged up or driven. Wiring them in parallel doesn't affect the CCA ability but does double the capacity.



    The Supra seems happier so far. Starter motor fires up more eagerly and my Oled has miraculously displays all the gear shift positions were it was flaky when selecting R before. The Oled program does need a final revision still to finish it. There are two grounds now for the batteries which must be helping, and the whole lot doesn't absorb any boot space other than a slight wiring bulge under the carpet.
    Mike
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    Work... what work? Club Member
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    That looks extremely neat. How are the batteries held in place?

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    Me? Post? Never! Club Member mattdavies's Avatar
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    This looks very neat and has got me thinking. are they both the PC950 pictured above ?
    1995 Silver BPU Auto - 1/4 Mile in 12.9secs @ 110mph

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    What search button? Club Member Delboy52's Avatar
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    The batteries are held in place only by the poly foam that I cut for a snug fit. I'll need to come up with something to go over the top of them to keep them absoloutly planted in place.

    They are Odessey Extreme PC950 (Extreme30) that were bought new as a pair. http://www.odysseybatteries.com/pc950.htm

    - Pulse (5-second) Hot Cranking Amps (PHCA) 950
    - Cold Cranking Amps (CCA) 400
    - 20Hr Nominal Capacity (Ah) 34
    - Reserve Capacity Minutes 60
    - Dimensions L x W x H (in) 9.8 x 3.8 x 6.1
    - Metric Dimensions L x W x H (mm) 250.0 x 97.0 x 156.0
    - Weight (lbs) 20.0
    - Weight (kg) 9.0
    Mike
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    '96 BPU TT Club Member Mk4Gaz's Avatar
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    I've been considering a battery relocation to the boot for ages, but not sure how much of a ball ache it is.
    That is a very neat setup though 👍🏻


  6. #6
    Got the shiny bug. Club Member ripped_fear's Avatar
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    Looks rather tidy, Great job! Is there anyway you could get them to sit a few cm lower you could then use a dremmel to cut some groves to lay the cables in to stop the bulge in the carpet. Also may be worth putting in a tie down god forbid you were ever in a smack you would want them to come flying out.
    I went from a 220bhp Sapphire Cosworth > Supra TT BPU circa 400 BHP......................BUt dont worry I had plenty of experiance on Mario Kart -scotty71
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    Rwarrrr Club Member Dim Sum's Avatar
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    Quote Originally Posted by Delboy52 View Post
    Recently I had a battery die on me by making the house stink of eggs (garage is integrated into the house). It had heated up, warped like a muffin and popped a cap.

    http://www.mkivsupra.net/vbb/attachm...5&d=1517180975
    http://www.mkivsupra.net/vbb/attachm...6&d=1517180975

    I thought this might have been due to me trickle charging it on a constant low voltage, but the settings on my Ctek charger were set to option 3 AGM which charges the battery less frequently but at a higher voltage. This is to lessen pronlonged heat build up from charging which these types of batteries have got issue with.

    So I replaced that battery with something even better, two of the same type! They are small and fit very discreetly in the sub well behind the seat. I have two as the previous one would be running out of power in a week if not charged up or driven. Wiring them in parallel doesn't affect the CCA ability but does double the capacity.

    http://www.mkivsupra.net/vbb/attachm...7&d=1517181667

    The Supra seems happier so far. Starter motor fires up more eagerly and my Oled has miraculously displays all the gear shift positions were it was flaky when selecting R before. The Oled program does need a final revision still to finish it. There are two grounds now for the batteries which must be helping, and the whole lot doesn't absorb any boot space other than a slight wiring bulge under the carpet.
    Like other members have said it's a very tidy setup. Where does the live cable come from? I have put the battery in the boot but the live cable comes from the rubber grommet in the boot near the fuel tank
    The White Dumpling Single turbo Precision 6765 84AR

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    What search button? Club Member Delboy52's Avatar
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    The batteries might fit in the gap laying down which would be even more hidden. I didn't do that because over time I imagined it might leak from one of the caps and I wouldn't know. If valleys were cut into the foam and maybe the terminal ends inverted so the cable was lower, that might hide the cables further I'll have another look at that.

    My old engine bay terminal ends were wired into a junction box near the old battery location I also have a Ctek plug wired in there so I can plug the car in to charge near the fuse box under the bonnet. The long 0 guage positive cable was fed behind the ABS pump, through the firewall where the OE loom goes, along the passenger door sill and rear bench seat into the boot area near the suspension turret. The negatives can be seen bolted to the chassis in front of the spare tyre. I didn't have to strip much away, just the plastic door sill strip where the rear washer pipe can be found. I fed it past the rear speaker whilst that was out so didn't have to pull internal plastics away.
    Mike
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    1UZ-FE VVTi 4.0 V8. Hybrid TT auto gearbox. Carbon wide arches. Brembo SRT8 conversion.

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    Rwarrrr Club Member Dim Sum's Avatar
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    Quote Originally Posted by Delboy52 View Post
    The batteries might fit in the gap laying down which would be even more hidden. I didn't do that because over time I imagined it might leak from one of the caps and I wouldn't know. If valleys were cut into the foam and maybe the terminal ends inverted so the cable was lower, that might hide the cables further I'll have another look at that.

    My old engine bay terminal ends were wired into a junction box near the old battery location I also have a Ctek plug wired in there so I can plug the car in to charge near the fuse box under the bonnet. The long 0 guage positive cable was fed behind the ABS pump, through the firewall where the OE loom goes, along the passenger door sill and rear bench seat into the boot area near the suspension turret. The negatives can be seen bolted to the chassis in front of the spare tyre. I didn't have to strip much away, just the plastic door sill strip where the rear washer pipe can be found. I fed it past the rear speaker whilst that was out so didn't have to pull internal plastics away.
    Thanks for the detailed walkthrough. I make do the same and change my layout this summer and this way at least the underside has one less cable running. I assume just put a plastic cover to make sure the positive cable is protected
    The White Dumpling Single turbo Precision 6765 84AR

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    What search button? Club Member Delboy52's Avatar
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    The positive cable has it's own 2-3mm thick insulation casing but where it passes anything hot in the bay, a bit of heat shielding wrap was added.
    Mike
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    1UZ-FE VVTi 4.0 V8. Hybrid TT auto gearbox. Carbon wide arches. Brembo SRT8 conversion.

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    What search button? MEMBERSHIP EXPIRED jagman's Avatar
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    I would add an inline fuse - due the battery being in the boot and a long unprotected cable run it’s normal to add a fuse :
    The Mini Cooper s has a boot mounted battery and they have a fuse block with a short positive cable ( a few inches), this will allow the fuse block (plastic square) to be placed alongside the battery .
    15 or so from any mini breakers .
    It would still look a tidy instal and offer protection against shorts

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    What search button? Club Member Delboy52's Avatar
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    Thanks Adam, I'll be adding that into the loop
    Mike
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    What search button? MEMBERSHIP EXPIRED jagman's Avatar
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    Mike - there are plenty of how to type guides on the Internet for rear battery installs , the problem is that most of them are wrong !!
    That's the power of the Internet .
    First is the fused pos line ,as mentioned - without this , it's possible destroy your car in smoke and fire as the complete line can get hot enough to melt the cable insulation along its length in a short circuit situation
    Second is the charge voltage from the alternator :
    The alternator uses the ALT S wire (alternator sense) this runs from a 7.5 a fuse to the battery , the alternator uses this to "sense" the battery voltage and adjust its output to match the charge state of the battery.
    Some of this is due to the temperature of the battery , in simple terms battery output voltage drops the hotter it gets -
    If charge voltage is too high battery life reduces .
    How much ? You can half it 10 years to 5 or even half it again to 2.5 years
    Temp wise circa 20-25 degrees c is the sweet spot ,but remember charge currents can heat a battery up .
    This is why they are usually fitted in a cool spot in the engine bay , or in the rear wing area in a rear mounted situation , the old V12 jags got so hot under bonnet ( cos its full of engine ) they fitted a battery fan !!!
    In your situation you have a much longer pos lead and it could drop voltage in the run to the front of the car , if the alt s wire is still connected here , it will see a reduced battery voltage and up the alternator output thinking the battery(s) is down a bit .
    A lesser factor is the central boot location may get quite warm on a long drive , dropping the nominal volts a tad and increasing the charge volts .
    So extend the alt s wire and run it to as close to the battery terminal as possible - here the inline fuse block is perfect , sorry a bit more wiring to run the length of the car - lol
    It is not essential and nothing will explode , but it may save you using more batteries than a Tesla

  14. #14
    What search button? Club Member Delboy52's Avatar
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    Excellent info, thank you. These batteries don't come cheap so I'd like them to last, and a bonus would be for them not to burst into flames! The Mini inline fuse unit should arrive anytime soon and I've plucked out where to find the Alt-S wire.
    Attached Files Attached Files
    Mike
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    Ride Or Die Club Member Supra-love's Avatar
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    That boot foam looks good mate, glad it worked ok for you! Nice install there
    In the words of sir Winston Churchill, Never, Never, Never, Give Up.

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