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Weird Dual Battery Problem (a little long)

Discussion in 'Chevy Trucks' started by markq, Dec 28, 2005.

  1. markq

    markq Member
    Messages: 47

    This is a little lengthy...............

    I have a couple questions about dual batteries, that I cant find the answer for.

    I recently added a second battery to my truck, and everything seems to be working properly. There are a couple of things that I am unsure about though, that I was hoping you all could help me out with!

    1. I didn't do anything with the stock battery (I think 600CCA), the battery I added is 770CCA. (they are isolated when not charging, so please don't tell me that they have to be the same build date, etc, so the new one doesn't discharge into the new one - I'm not concerned about this) My question is this: I was recently told that both batteries should be the same CCA - is this a concern? I plan to replace the stock battery with a matching one (770CCA) at some point, but don't want to mess anything up in the meantime. If this is a problem, can someone explain why GM offers an option for dual batteries where the stock is 770CCA, and the aux is 600CCA? (RPO = 8B0 (Batteries, 770 CCA with a 600 CCA auxiliary)

    2. The isolator that I am using is connected to switched power, so that it only connects the 2 batteries when the ignition is in the acc/on position. My truck starts just fine with the one battery, but when its cold, it does sound a little sluggish. I expected this dual battery setup to fix that (but not the only reason I did it). <--- didn't happen! Now my thoughts are this....when the ignition switch is turned to the acc/on position, the isolator is engaging and connecting the batteries....just like the radio, turn signals, AC, wipers, etc work when the switch is in the acc/on position.....however, all of these go off when the switch is turned to the start position to turn over the engine (presumably to keep them from being damaged from voltage drops, and spikes) - does this mean that the power to the isolator is being cut off, thereby isolating the batteries when I turn the engine over? This would explain why there is no difference in how the engine starts when cold. If this is the case, how can I fix it so that the isolator gets power, not only in the acc/on position, but also in the "start" position?

    For those of you that took the time to read this book, and respond.........THANKS!!!!!!!!! :)
  2. TLS

    TLS PlowSite.com Addict
    Messages: 1,425

    In answer to your question.... Why don't you try it and see? Hook up a voltmeter to your switched power source, then start and see if it drops to 0 when starting?

    This is mainly the reason so many of us suggest making a permanent parallel dual battery system.

    To me, GM's gasser dual battery system is geared for slide in truck campers allowing you to fully drain the aux. battery and still start the truck in the morning.

    I don't think the solenoids used for this switched connection are designed for FULL amperage starting power (I may be wrong on this).

    I was never happy with GM's dual battery system on my '90 Chevy. The wiring used was thin gauge and the solenoid wasn't very HD. I later switched over to a parallel system and never looked back. To me, a full parallel system doesn't have ANY drawbacks.
  3. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    I did the dual battery setup with an isolator years ago. Hated it. Now I run them in series. I can still kill them, but a lot less problems than isolated. Isolators work great on paper.
  4. JohnnyU

    JohnnyU 2000 Club Member
    Messages: 2,040

    I think you mean parallel, series would yield 24 volts. Parellel would be positive to positive, negative to negative, effectively doubling your reserve capacity and available cranking amps.
  5. calhoun

    calhoun Senior Member
    Messages: 165

    I don't know why 2 dif size batteries are used. (I have the 8BO option).

    The aux battery is not meant to help start the vehicle. If this is why you have duals you should not use the isolator. The isolator is for people that use power while the truck is off (I have a 2500watt inverter for power tool use) and want to be sure we can start, the truck, at the end of the work day. If the 2 batteries where connected, for starting, it would make it even harder to start since the main battery would be trying to start plus trying to charge the aux. I think the factory isolator only connects to the main when there is alternator output.
  6. TLS

    TLS PlowSite.com Addict
    Messages: 1,425

    Mark Q,

    How did you make out with this?
  7. markq

    markq Member
    Messages: 47

    I didnt install the aux battery to help start the truck. I installed it becasue I run a plow, extra lights, and next year will be running a salter/sander. Wanted to have the extra power when running all the other equipment. I just expected it to help with the starting......after thinking about it, and reading the posts, it doesnt seem like that is happening, but again, not a big deal. It starts every time with one battery, and I do like the isolated setup.

    My biggest concern was the batteries being different capacities.....someone said this was a bad idea, and I wanted to see what everyone else thought about it. I dont think that GM would have an option for dual batteries with different capacities if it was bad for the batteries.

    Thanks everyone for the replies!!!!
  8. TLS

    TLS PlowSite.com Addict
    Messages: 1,425

    On GM's diesel trucks (hooked direct in parallel) the batteries are matching CCA delco's.

    Even though your setup is similar to GM's GASSER dual battery (camper style solenoid connection), it is still a good idea for both batteries to be of the same type/age/CCA's. As they are connected while the truck is in operation (charging). A battery of lesser capacity will bring down the battery of greater condition.
  9. cincy snowdog

    cincy snowdog Senior Member
    Messages: 262

    been there done that do yourself a favor take the isolator off,buy a new battery like your other new one you have run them together and you will be happy ever after .
  10. lawnmedic

    lawnmedic Senior Member
    Messages: 703

    We have 1 2001 2500HD with the factory duel battery option. The isolator keeps the batteries separated. The batteries are never truly connected. this is the same system used in motor homes. The batteries can be different sizes because the isolator charges the primary battery first, then charges the secondary battery.
    If there is a large load being placed on the primary battery circuit(headlights, defroster, wipers, radio, etc.) the secondary battery will be very slow to charge.
  11. PlowingHD

    PlowingHD Junior Member
    Messages: 26

    Anyone with a new body style pickup (HD/STD 3/4 ton) that has dual batteries the batteries are wired in paralell, unlike the classic body style. If you look the main bat + cable on the aux. goes directly to the starter, which is connected to the main battery. Someone correct me if im wrong please.
  12. PlowingHD

    PlowingHD Junior Member
    Messages: 26

    To answer the question about CCA's i believe that the only effect it will have on the charging system is that each battery will have a different charging rate, the bigger the CCA's the longer it will need to charge to bring the specific gravity back up to 1.26
  13. Bad Luck

    Bad Luck Senior Member
    Messages: 741

    Still a firm believer that for our main use, plowing and such, dual batts should be run together. For the cost of isolating them, if you are really concerned with not being able to start your truck pick up a jump pack from Sears. By isolating the battery you are not giving yourself the extra reserve of the second battery. If your isolator is a switched source, you are not using both of your batteries to start the truck. Where did you get the power to turn on the isolator?

    BTW - I added a second battery to my truck, and I keep a small battery post wrench in my glove box. If I ever use any accesories (stereo, lights, ect) for a LONG period of time (which almost never happens) I just pop off the cables so I'll still have a good charge to start it.
  14. calhoun

    calhoun Senior Member
    Messages: 165

    You asked so I will tell you. This is not correct. There are at least 3 diff dual battery options available. Only one is in parallel the others involve isolators with various battery configurations. If you order a D-max it only comes with the parallel hook up but all others you pick the option.

    If you have factory duels RPO TP2 is a parallel hookup and RPO 8B0 is one of the isolated options.
  15. TLS

    TLS PlowSite.com Addict
    Messages: 1,425

    Gas or Diesel?