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Old 07-06-2016, 10:29 AM   #1
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Battery Tender Install Questions

I'm not getting a response from the manufacturer so hopefully someone here has experience with battery Tenders. I just purchased our first travel trailer, new from the dealer. It has two Interstate HD24-DP 12v batteries connected in parallel and they are located inside plastic battery boxes on the A-frame just behind the propane tanks, so technically "outside" of the trailer. Based on the install instructions I am assuming this set-up is considered "when battery is outside vehicle". Instructions tell me to connect the red hot lead to the positive terminal on the battery and the negative lead to a 24 inch long 6-gauge battery cable that is then connected to the negative battery post.

My neighbor who has had many travel trailers and currently also uses the Tender Junior (he recommended it to me) just simply connected the red tender lead to the positive post of one of the two batteries and the negative lead to the negative post of the same battery. So essentially we have the tender connected directly to just one of the batteries without the 24 inch extra negative cable.


1) Is this connection correct? If not, what is the correct connection? I plan to leave the tender connected indefinitely during the summer while the trailer is parked on our RV pad at home.

2) What is the purpose/need of the 24 inch extension?

3) Will this connection charge both batteries at the same time?


Thank you for any assistance. I just don't want to create any potential hazards or issues!
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Old 07-06-2016, 10:58 AM   #2
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This should help:
Battery School | Batteriesnorthwest.com | Connect Your Batteries for Optimum Efficiency
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Old 07-06-2016, 11:00 AM   #3
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Quote:
Originally Posted by tgduffy View Post
I'm not getting a response from the manufacturer so hopefully someone here has experience with battery Tenders. I just purchased our first travel trailer, new from the dealer. It has two Interstate HD24-DP 12v batteries connected in parallel and they are located inside plastic battery boxes on the A-frame just behind the propane tanks, so technically "outside" of the trailer. Based on the install instructions I am assuming this set-up is considered "when battery is outside vehicle". Instructions tell me to connect the red hot lead to the positive terminal on the battery and the negative lead to a 24 inch long 6-gauge battery cable that is then connected to the negative battery post.

My neighbor who has had many travel trailers and currently also uses the Tender Junior (he recommended it to me) just simply connected the red tender lead to the positive post of one of the two batteries and the negative lead to the negative post of the same battery. So essentially we have the tender connected directly to just one of the batteries without the 24 inch extra negative cable.


1) Is this connection correct? If not, what is the correct connection? I plan to leave the tender connected indefinitely during the summer while the trailer is parked on our RV pad at home.

2) What is the purpose/need of the 24 inch extension?

3) Will this connection charge both batteries at the same time?


Thank you for any assistance. I just don't want to create any potential hazards or issues!
One battery tender is really not designed for two batteries so I'm not sure how well it would work. But if I was using one I would connect the negative to one battery then the positive to the other battery.
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Old 07-06-2016, 11:05 AM   #4
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Originally Posted by ilmor View Post
One battery tender is really not designed for two batteries so I'm not sure how well it would work. But if I was using one I would connect the negative to one battery then the positive to the other battery.
My Battery Minder will handle 3 batteries at the same time.

I think you can hook red to positive and black to negative. Either battery as they are connected in parallel.

I've had GREAT results with this product. My tractor and motorcycle batteries last 8 to 10 years. This should be perfect for maintaining your deep cycle batteries. The anti-sulfation technology is great.
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Old 07-06-2016, 11:05 AM   #5
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A Tender is not a 'fast charger'. It takes a while, but if it is a "smart" tender it will sense a full charge and shut off, or go into maintenance mode. I use the Battery Tender on my ATV battery, since it is just one 12v battery. But no matter how many batteries you connect in parallel, your system (if in parallel) is 12V.

On my boat, however, I have a Minnkota 3 bank charger. I have two batteries in series for my 24v trolling motor, and one 12v battery for starting the outboard. But I ran each of the 3 separate leads to each of the 3 batteries. Works best that way.

Battery Tenders are about $20 (?) or so......if I was going to do what you are, I'd simply get two battery tenders, one for each battery. Note that most of the cheaper ones don't give much if any readout as to percent charge. My Minnkota charger indicates percent charge (via LED lights, not any actual readout).

If you plug to your house with a 30 amp plug (electrician installed ours), you'll be charging all the batteries via the camper itself.........won't need the tender.
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Old 07-06-2016, 11:31 AM   #6
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Originally Posted by BandJCarm View Post
A Tender is not a 'fast charger'. It takes a while, but if it is a "smart" tender it will sense a full charge and shut off, or go into maintenance mode. I use the Battery Tender on my ATV battery, since it is just one 12v battery. But no matter how many batteries you connect in parallel, your system (if in parallel) is 12V.

On my boat, however, I have a Minnkota 3 bank charger. I have two batteries in series for my 24v trolling motor, and one 12v battery for starting the outboard. But I ran each of the 3 separate leads to each of the 3 batteries. Works best that way.

Battery Tenders are about $20 (?) or so......if I was going to do what you are, I'd simply get two battery tenders, one for each battery. Note that most of the cheaper ones don't give much if any readout as to percent charge. My Minnkota charger indicates percent charge (via LED lights, not any actual readout).

If you plug to your house with a 30 amp plug (electrician installed ours), you'll be charging all the batteries via the camper itself.........won't need the tender.
Just be careful with leaving it plugged into the house. The converter may not have the capability to sense full charge and will cause an overcharge condition. In this instance a good battery maintainer is a better choice.
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Old 07-06-2016, 12:21 PM   #7
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As an electronics tek since '58 and an EE since '67.....I never saw the requirement for a battery "tender".

Also.....the guys at battery school are putting out BS.

They show separate drawings of two batteries and claim one is more efficient than the other......NOT !
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Old 07-06-2016, 12:36 PM   #8
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Originally Posted by acadianbob View Post
My Battery Minder will handle 3 batteries at the same time.

I think you can hook red to positive and black to negative. Either battery as they are connected in parallel.

I've had GREAT results with this product. My tractor and motorcycle batteries last 8 to 10 years. This should be perfect for maintaining your deep cycle batteries. The anti-sulfation technology is great.
I'll echo these points. I've had the same battery tender hooked up just like this to my two dump trailer batteries for over six years now --- never had an issue.
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Old 07-06-2016, 12:44 PM   #9
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1, The "DP" (Dual Purpose) series is not a true deep cycle and only has about 75AH capacity per battery in a group 24 size.

2. A single tender should be fine.

3. The batteries should be fully charged by a converter or external charger before being stored with a maintainer.

4. This battery chemistry should get an "Equalization Charge" from time-to-time.
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Old 07-06-2016, 12:52 PM   #10
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a Battery Tender is an excellent choice, even on parallel battery connections (pos to pos and neg to neg)...

Been using one for many years on boat battery, and have been very happy.

at the low currents that the battery tender supplies, the resistance of the connecting wires between the batteries should be negligible...

If you have any doubts, disconnect one wire from one of the batteries hooked in parallel, and use the Tender on each battery, alternating Tender connections from one battery to the other every 2 or 3 weeks. That way each battery gets what IT needs without consideration of another.

When you do have to replace any battery, always replace in NEW pairs with two identical batteries.

Quote:
Also.....the guys at battery school are putting out BS.

They show separate drawings of two batteries and claim one is more efficient than the other......NOT !
If you were pulling large load currents, like 80-100 amps or more (starting a large auto engine), the parallel connection shown in the battery school picture could present a problem in unequal battery efficiency, but at low load currents like 10-30 amps in your camper using large (typical 2 gauge connector wires) wires between the batteries, efficiency should be for all practical purposes equal.

My 2cents worth...
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Old 07-06-2016, 01:09 PM   #11
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Thanks everyone for your replies. So it appears how I have the tender connected is OK. Why would the instructions that came with the tender request I use a 2 foot extended cable to the negative terminal? Right now I just have the two connectors hooked directly to one of the batteries, not the clip type but the connectors that actually fastened below the nut on the battery terminals.
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Old 07-06-2016, 01:17 PM   #12
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Originally Posted by tgduffy View Post
Thanks everyone for your replies. So it appears how I have the tender connected is OK. Why would the instructions that came with the tender request I use a 2 foot extended cable to the negative terminal? Right now I just have the two connectors hooked directly to one of the batteries, not the clip type but the connectors that actually fastened below the nut on the battery terminals.
My best guess is that they are trying to insure that the two leads of the unit don't touch.

Lawyers.
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Old 07-06-2016, 01:31 PM   #13
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I did a search for Battery Tender manual, read 3 different files and found nothing that specifies a 2 foot cord...

What exact model are you using?

however one piece claimed it would...

Simultaneously charges and / or maintains
up to 5 or 10 batteries !!
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Old 07-06-2016, 01:33 PM   #14
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It's item 16(b) on this:

http://www.batterytender.com/021-0128-man.pdf
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Old 07-06-2016, 01:59 PM   #15
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OK, so on Page 4 they claim:

Quote:
ATTENTION: The Battery Tenderģ Plus CHARGER HAS A SPARK
FREE CIRCUITRY. The output alligator clips or ring terminals will not
spark when they are touched together.
Then they have you attach a 24 inch long lead as a:

FOLLOW THESE STEPS WHEN BATTERY IS OUTSIDE VEHICLE. A SPARK NEAR
THE BATTERY MAY CAUSE BATTERY EXPLOSION. TO REDUCE RISK OF A
SPARK NEAR BATTERY:
a) Check polarity of battery posts. POSITIVE (POS, P, +) battery post usually has a
larger diameter than NEGATIVE (NEG, N, Ė) post.
b) Attach at least a 24-inch-long 6-gauge (AWG) insulated battery cable to NEGATIVE
(NEG, N, Ė) battery post.

Sounds like their lawyer made them put this in...
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Old 07-06-2016, 03:46 PM   #16
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So I heard back from the Battery Tender folks. They said "You would need to connect positive to one battery and negative to the second battery. Do not connect to just one battery. The Jr is most likely not enough charging amps for both of those batteries. I would recommend using nothing less than 1.25 amp. Battery Tender Plus."

Do I really need to connect to both batteries even though they are in parallel, or are they just trying to sell me on a bigger tender?

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Old 07-06-2016, 03:56 PM   #17
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Just connect each lead to each battery. Pos to one neg to the other you will be fine. As long as bats are full charge when you connect tender, you will be ok. I have been using these tenders for years and they do a fantastic job.
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Old 07-06-2016, 03:57 PM   #18
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I finally did hear back from the manufacturer. They want me to attach the positive to one battery and the negative to the other battery. They also commented that the Tender Junior may not be large enough for my two 12v batteries. I would really like to just keep things the way they are. Feedback?
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Old 07-06-2016, 04:01 PM   #19
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Just connect each lead to each battery. Pos to one neg to the other you will be fine. As long as bats are full charge when you connect tender, you will be ok. I have been using these tenders for years and they do a fantastic job.
What he said!
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Old 07-06-2016, 04:11 PM   #20
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Sorry but I need to clarify. Follow the manufacturer by attaching the positive tender lead to battery A's hot and the negative tender lead to battery B's negative post? How is this different from my current connection of both pos and neg to the same battery?
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