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  1. #1
    Senior Chief Petty Officer scooper77515's Avatar
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    Default Can I use trickle charger on two batteries connected with jumper cables?

    I assume so, but wanted to make sure the jumper cables don't cause an issue. 16' long.

    I have not set up a dual battery switch at this time (got boat on Tuesday), so I just carry a spare car battery in the boat, and keep it charged on a trickle charger. Then if the stereo kills the battery on the water (or I leave depth-finder on over the work week as previous owner did before giving me the boat) I can just use the jumper cables to start the boat. Then it recharges the main battery in a few minutes of driving.

    Anyway, will the 2A trickle work over 16' cables?

    I will put in a switch, but that will be a winter project. Don't want the boat out of the water right now. Just starting to get less humid weather and this is our prime boating season.

  2. #2
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    Jumper cables will work fine, but they are a bit bulky. A pair of thin clip(wires with "alligator clips" on each end) leads will work better.

  3. #3
    Moderator Bob_VT's Avatar
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    Do not use the trickle charger connected to two batteries at once or it will not work. A 2A charger is only for one battery at a time. They make dual bank chargers but two trickle chargers are cheaper and just make sure the batteries are not connected while charging
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  4. #4
    Petty Officer 1st Class jusfloatin's Avatar
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    Quote Originally Posted by Bob_VT View Post
    Do not use the trickle charger connected to two batteries at once or it will not work. A 2A charger is only for one battery at a time. They make dual bank chargers but two trickle chargers are cheaper and just make sure the batteries are not connected while charging
    Sorry but I do not understand that.
    What would be the difference, the trickle charger only puts out what it is rated for. ( + or - a wee bit )
    Unless you are taking about the fact of how long the charger will have to be left on to fully charge 2 batteries compared to 1.

    I run two Wallymarts dual use deep cycles that are hooked in parallel.
    I use an old K-Mart 3 amp trickle charger.

    Plug it in Sunday night and by Thurdays it is fully charged.
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  5. #5
    Senior Chief Petty Officer scooper77515's Avatar
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    I wasn't sure if the extra flow needed to go through the cables would overburden the charger. Or not sure if 2 12-volt batteries equals one 24-volt, overburdening the charger. (I took college electronic physics back in college, but never used it, so I losed it )

    I don't really need to charge both, since one gets charged by the alternator during use. I just figured if I had the charger, I could "tend" them both over the winter with one charger and the jumper cables.

  6. #6
    Petty Officer 1st Class jusfloatin's Avatar
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    Quote Originally Posted by scooper77515 View Post
    I wasn't sure if the extra flow needed to go through the cables would overburden the charger. Or not sure if 2 12-volt batteries equals one 24-volt, overburdening the charger. (I took college electronic physics back in college, but never used it, so I losed it )

    I don't really need to charge both, since one gets charged by the alternator during use. I just figured if I had the charger, I could "tend" them both over the winter with one charger and the jumper cables.
    It would be 24 volts if hooked in series like a flashlight.
    It will be 12 volts if in parralel pos to pos neg to neg.

    Overburdening- what would be the difference if it was hooked up to 1 battery that was completely dead or two that were not.

    Durring the off season here all equipment not used get hooked to the trickle charger once a month ( boats / ATV's / snow blower/ skidoo )

  7. #7
    Supreme Mariner Silvertip's Avatar
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    You have several things going against you. 1) time 2) distance, and 3) output. TIME: The output of the trickle charger will determine how long it takes to top off two batteries. The amount of time can be determined if you know roughly how much was sucked from the batteries over a given time period. It's not practical to keep track of that so for the health of the batteries, it is best to top them off as quickly as possible. You can safely charge flooded batteries at rates up to 20% of the AHr rating. Trickle charging a nearly stone dead battery is better than not charging it at all but a higher output charger would be best. DISTANCE: Depending on the quality of the jumper cables, 16 feet of cable may or may not be a factor in lowering the voltage from the charger at the battery. You can use jumper cables to parallel two batteries. It is after all -- just wire. OUTPUT: A 2A trickle charger on two batteries will take many hours to actually "charge" a battery. And by the way, your engine will not fully charge a nearly dead starting battery in a few minutes of running. It may restart the engine after a few minutes, but it is far from being fully charged. The term "trickle charger" is really a misnomer in that they are really "Maintainers" and are intended to simply keep a battery topped off or for use on much smaller batteries like motorcycle and lawn tractor batteries. For batteries that don't get deeply discharged then a maintainer is fine. For trolling motor batteries that do get deeply discharged, their health and long term survival depends on proper charging and a trickle charger is not the way to charge them.

  8. #8
    Petty Officer 1st Class jusfloatin's Avatar
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    Quote Originally Posted by Silvertip View Post
    You have several things going against you. 1) time 2) distance, and 3) output. TIME: The output of the trickle charger will determine how long it takes to top off two batteries. The amount of time can be determined if you know roughly how much was sucked from the batteries over a given time period. It's not practical to keep track of that so for the health of the batteries, it is best to top them off as quickly as possible. You can safely charge flooded batteries at rates up to 20% of the AHr rating. Trickle charging a nearly stone dead battery is better than not charging it at all but a higher output charger would be best. DISTANCE: Depending on the quality of the jumper cables, 16 feet of cable may or may not be a factor in lowering the voltage from the charger at the battery. You can use jumper cables to parallel two batteries. It is after all -- just wire. OUTPUT: A 2A trickle charger on two batteries will take many hours to actually "charge" a battery. And by the way, your engine will not fully charge a nearly dead starting battery in a few minutes of running. It may restart the engine after a few minutes, but it is far from being fully charged. The term "trickle charger" is really a misnomer in that they are really "Maintainers" and are intended to simply keep a battery topped off or for use on much smaller batteries like motorcycle and lawn tractor batteries. For batteries that don't get deeply discharged then a maintainer is fine. For trolling motor batteries that do get deeply discharged, their health and long term survival depends on proper charging and a trickle charger is not the way to charge them.
    How big of charger would you suggest for the health and long term survival of two deep cycle batteries hooked together in parallel?

  9. #9
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    Problem with 2 batteries in parallel is you will only charge as much as the worst battery will take. It will bring down the better battery NOT bring up the low one.

    A Perco dual battery switch would not require boat removal from the water.
    it's a simple job just need a few extra cables for hookup.
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  10. #10
    Senior Chief Petty Officer scooper77515's Avatar
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    Neighbor came over today to check out the new boat and when i lifted the engine cover, I noticed that there is plenty of room for the second battery right near the first one, and then there is a chunk of plywood "firewall" behind the rear seat that would require only a short chunk of wire to put in the A-B-Both switch. So, yes, it would be a quick job.

    And one that will be done soon.

    Still would like to trickle charge them to maintain them over the winter...

  11. #11
    Senior Chief Petty Officer scooper77515's Avatar
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    Bought the A-B-ALL-Off switch and the battery box. Gathering the materials needed to install it. Will probably lose the boat this weekend due to getting custom bimini installed, but should have all the stuff by the time it gets back and get into installation.

    Gotta search for a How To thread. Looks easy and straightforward, but no doubt someone has hit a snag and I can learn from their mistake(s).
    2003 Glastron GX 185, with VolvoPenta 4.3GL, currently running Stilleto Baypro III 14.25X21 at 46 mph and 4400 rpms. Other props were 3-blade aluminum 14.3X23 at 43 mph and 4400rpm, and 14.3X21 at 49mph at 4800 rpms.

  12. #12
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    You can get a dual bank in boat charger for 100 bucks and solve this problem entirely. My opinion is its dangerous to try and charge 2 batteries connected in parallel... unless both batteries are at exactly the same charge. You are either over charging one or under charging the other. A dual bank charger isolates the two batteries and avoid overcharging/overheating one of them.
    Mike

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  13. #13
    Supreme Mariner Silvertip's Avatar
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    Default Re: Can I use trickle charger on two batteries connected with jumper cables?

    Battery chargers cannot sense which battery in a parallel system is charged and which is not. The charger monitors "system voltage". During the charging cycle the weaker battery holds down the system voltage until both batteries are equal and then they charge in unison. Obviously if one battery is defective in any way, then and only then would the system not reach full charge. If both batteries are functional, even if they are different capacities, they will charge just fine. If that were not the case, over the road trucks would not have six batteries in parallel.

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