Why does my diesel pickup truck have 2 batteries? is it still 12 volts? could i jump something if i needed to?

Any info that you could tell me would be helpfull. it is a 2004 chevy silverado 3500 (duramax diesel 6.6L)

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5 Responses to Why does my diesel pickup truck have 2 batteries? is it still 12 volts? could i jump something if i needed to?

  1. guess78624 June 13, 2009 at 11:12 am #

    It has 2 batteries, – because one battery can not provide enough cranking amps to start the engine (dependably)! The batteries are connected in "parallel", – which means that you still have the 12 volts the same as everybody else! I might add, – if you need to replace these batteries (one or both), – get the highest "amp output" battery that can possibly be mounted in the provided place! You need all the amps possible when the temperature "really gets down there!"

    Another warning here, – do not try to continue to start engine when batterys are very low, – you can burn out the starter, as it actually draws more amps cranking "slow" with reduced voltage, – than cranking fast with proper voltage! This is a $250 to $500 "mistake"!!

    Be aware though that the "cheap jumper cables" you buy everywhere are about useless to actually "jump start the truck! They are capable of carryng 10 to 30 amps usually!, – Your truck probably requires around 450-500 amps on a "nice warm day", – maybe 750 amps on a "cold day",- when the temperature is well below "0"! So you can leave jumpers hooked up with another vehicle running, and "warm up the batterys", and charge them some (if possible), – but the cables will quickly start to "smoke" when you start cranking! You have really fat insulation, but thin wires! Maybe 8 gauge (on most cables)! So if you want to be prepared for really "Jump starting" your truck, – you are going to have to go to somewhere that sells the jumper cables that the "big truck drivers use"! These cables have "00" gauge wire or bigger, — (1/2" dia wire,– or bigger, – as compared to maybe 3/16" wire). These will probably cost you in excess of $50, so you will want to store them carefully and take care of them! You don't want to be buying them often!

    Note: actually one battery will not dishaarge into the other – unless the second batery is not good anymore! The bigger battery will provide somewhat more amps while cranking, but if the "450 amp battery" – is capable fo putting out 450 amps yet, — and the "new 550 amp battery" is fully charged, — they will still put out 12 volts, and the amperage required to crank the starter will still remain the same!

    Technically the starter will draw a little more amperage out of the "bigger battery". The "Cranking time" will still be longer than two of the same sized (good) batteries would be!! When the charging system brings the back up to full charge, the larger battery will charge slightly longer (or faster) than the smaller one! However they will both charge to proper levels, and then "taper off" to low "maintainance rate" from there on!

    Or simply put you will not have any problems! The only thing you have to worry about is putting in batteries too small to do the job,- in which case they will go "down" very rapidly! A smaller battery againast a bigger battery decreases cranking time!

  2. Donald H June 13, 2009 at 11:12 am #

    Your diesel has two batteries because diesels are notoriously hard to start when they're cold. The batteries are wired in parallel so it's still 12 Volts (Just more cranking Amps). My duramax has a place specifically made for jumping. It's a little red box just inboard of the left battery. On top is a metal plate for attaching the ground. Mine's 2006 so I'm not sure yours has the same thing. Your answer is a definite yes. You could connect to one of the batteries just as you would any other car.

    Hope this helps.

  3. Wisdom June 13, 2009 at 11:12 am #

    Donald is correct. Just remember when replacing a bad battery, to replace both with the same type and power.
    One can discharge into the other!

  4. Mohammad June 13, 2009 at 11:12 am #

    NO, it is 24 volts and they are connected in series, that is you can jump an alike car which have two batteries too, or you may jump a normal car ,,,but you have to use one single batterie of yours by it self,,,,,remember that jumping another car MAY
    spoil ur car computer.

  5. dieselmech2 June 13, 2009 at 11:12 am #

    These days Diesel are not that hard to start anymore as bad as they was years ago because of intake heaters and glow plugs.
    ONE BIG QUESTION TO MOHHAMMAD
    (NO, it is 24 volts and they are connected in series, that is you can jump an alike car which have two batteries too, or you may jump a normal car ,,,but you have to use one single batterie of yours by it self,,,,,remember that jumping another car MAY spoil ur car computer.)………. SO IF I HAVE A SEMI THAT HAS 4 BATTERIES THAT MEANS I HAVE 48 VOLTS??????
    I have seen one 24 volt system in a 1984 Blazer and it come from the military. No it is still 12 volt.