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  1. #1

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    Dual batteries require dual battery tenders?

    I'm adding a deep-cycle battery for my house loads (stereo, depth finder, george foreman grill), a starter battery for the engine with a Perko switch for 1-2-both-off action. Can I connect the tender to both batteries at the same time? I read thru the tender manual and didn't see anything about it either way. My guess is that each batt needs it's own tender, but I figured it was worth a shot.

    Thanks
    Cameron


  2. #2
    AKA: Larry lafjax's Avatar
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    Quote Originally Posted by ausgezeichnet7 View Post
    I'm adding a deep-cycle battery for my house loads (stereo, depth finder, george foreman grill), a starter battery for the engine with a Perko switch for 1-2-both-off action. Can I connect the tender to both batteries at the same time? I read thru the tender manual and didn't see anything about it either way. My guess is that each batt needs it's own tender, but I figured it was worth a shot.

    Thanks
    Cameron
    I do not see why not!! It would see the batterys as one, like they were connected in parallel. The output to each battery would be 1/2 but it's just a tender, you are not doing deep re-charging, etc. I would try it out..I would leave it connected all the time you are out of the water.

  3. #3
    2008 RXP-X
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    Get a dual bank battery charger. The better ones have intelligent charging and can concentrate more of the charging amps one one or spread across both batteries.

  4. #4

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    Quote Originally Posted by lafjax View Post
    I do not see why not!! It would see the batterys as one, like they were connected in parallel. The output to each battery would be 1/2 but it's just a tender, you are not doing deep re-charging, etc. I would try it out..I would leave it connected all the time you are out of the water.
    I guess I was curious moreso as one is a deep-cycle and the other is a starter so they have different charge rates... however I think you're right, the tender charges slowly enough that I don't think it will matter.

    Quote Originally Posted by X-Man View Post
    Get a dual bank battery charger. The better ones have intelligent charging and can concentrate more of the charging amps one one or spread across both batteries.
    That's definitely the safe way to go. I already have a battery tender, otherwise I would have gotten a dual bank model. I might still get another one.

  5. #5
    AKA: Larry lafjax's Avatar
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    Quote Originally Posted by ausgezeichnet7 View Post
    I'm adding a deep-cycle battery for my house loads (stereo, depth finder, george foreman grill),
    Thanks
    Cameron
    Cameron, are you hooking the 2nd battery into the seadoo electrical circuit for charging purposes while riding? This might be a problem. The ecu is looking for a certain load and it might screw it up with too much amperage. I hooked up a 17 amp gel cell to replace my stock battery and I got error codes about low power. Not sure the ski charging circuit will handle both batteries together??

  6. #6

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    Quote Originally Posted by lafjax View Post
    Cameron, are you hooking the 2nd battery into the seadoo electrical circuit for charging purposes while riding?
    The current plan is to not charge them together on the water, but I was considering using an integrator that keeps them isolated and prioritizes the starter. I have no idea how much the ECU really does on my boat (2003 Sportster LE - dual carb)

    How did you resolve the problem with your battery?

  7. #7
    1996 Sea Doo Challenger (787x1)
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    Quote Originally Posted by lafjax View Post
    Cameron, are you hooking the 2nd battery into the seadoo electrical circuit for charging purposes while riding? This might be a problem. The ecu is looking for a certain load and it might screw it up with too much amperage. I hooked up a 17 amp gel cell to replace my stock battery and I got error codes about low power. Not sure the ski charging circuit will handle both batteries together??
    I added a second full-size (Grp 34 I believe) battery to my `96 Challenger (1 x 787) in September last year; it's been running fine with only a 1/2/1+2 switch between the batteries and engine. No problem with charging both batteries simultaneously, as of yet; they'll automatically balance with the majority of charge going to the lower voltage battery. I've kept a 5 watt solar panel on each battery between uses, and it hasn't needed a plug-in charge since last fall.

    I know there is a lot of newer technology out there, and I enjoy my share of it...in this application, however, I haven't been able to discern any benefit from adding anything beyond the Perko-style switch...and it's all been working great.

    AFA running the tender on both at once--the tender is basically an intelligent trickle-charger that shuts off when the battery is fully charged, yes? I'd guess you could get away with using it to *maintain* two already-charged batteries...connecting it to two *dead* batteries might fry it (and your boat).

    You might consider locating the tender outside the boat, the first time you try it...just to give yourself a bit of insurance.

  8. #8
    AKA: Larry lafjax's Avatar
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    Quote Originally Posted by ausgezeichnet7 View Post
    How did you resolve the problem with your battery?
    Ha! I just bought a 30 amp battery and did not use the 17 amp one.

  9. #9
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    from batterytender.com

    14. Can the Battery Tender Plus battery charger be used to charge more than 1 battery simultaneously if the batteries are connected in parallel?

    Yes, the Battery Tender Plus battery charger can be used to charge more than 1 battery simultaneously when those batteries are connected in parallel. Theoretically, there is no reason that you cannot recharge your batteries in parallel, or that you canít use a larger battery. HOWEVER, you must recognize that the amount of time required to recharge may be much longer than you would normally expect. Effectively, by charging more than 1 battery in parallel, the charger behaves as if one larger battery is connected to its output terminals.

    The Battery Tender Plus only puts out 1.25 Amperes. That means it will take over 24 hours to recharge a 32 Ah battery to 80%, assuming that is fully discharged. It will take another 12 to 24 hours on top of that to recharge the last 20%. If you put an even larger battery in parallel with it, then the total times may double or triple. That is not a reason for concern.

    The real concern is that the Battery Tender Plus will only switch over from 14.4 VDC absorption voltage when the current draw from the battery drops below 0.1 amps or after an 8-hour period in absorption mode. Under normal circumstances, with battery capacities up to 32 Ah, this is a good thing and the Battery Tender Plus will switch over to the long-term storage voltage of 13.2 VDC with no problem. In fact, it usually turns out that the amount of time spent at the constant voltage of 14.4 VDC, typically a few hours, is good for the battery, especially the newer AGM style batteries. There is a maximum time limit of 8 hours at 14.4 VDC. As long as the charger switches over to 13.2 VDC before the 8-hour timeout, then the battery will be 100% recharged. However, the larger the battery that you try to recharge, the higher likelihood that the charger current will never drop below 0.1 amps with 14.4 VDC applied, no matter how long the charger is connected. That means that the charger output will remain at 14.4 VDC for the maximum time period of 8 hours. This is also not a problem for the battery in terms of "dry-out", but again with the larger batteries if the charge current has not been reduced to a maximum of a few tenths of amps, then there is a good possibility that the battery will not be 100% recharged before the switchover to 13.2 VDC. This will result in even more time required before 100% recharge is achieved.

    Our recommendation is that you not charge batteries in parallel, again assuming that the batteries are 100% discharged. If the batteries are only partially discharged, then it is probably OK to charge them in parallel.


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