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Old 01-08-2021, 11:05 AM   #1
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Trickle Charge 3 AGM At The Same Time, Same Charger?

I take my AGM batteries out for the winter and trickle charge them separately from each other. I use a Schumacher SC-1280 charger which has 15A and 3A trickle charge. I switch the charger from battery to battery over the winter. It would be easier to connect them all in parallel and trickle charge the whole bunch at once. I contacted Schumacher and asked if this was possible. Supposedly I can, but this was the response:
"Good Morning ,
Thanks for contacting Schumacher Electric Corp. about your model SC1280.
Yes sir the unit is a trickel charge battery once its fully charge the battery charger will maintian/trickel charge the battery giving the unit a small current once needed without damaging the battery."
It obviously doesn't address the trickle charge 3-batteries-at-once I would like to do. I was hoping that someone here has addressed this same issue (hopefully with the same charger) so I can get a definitive answer, and not just speculation.
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Old 01-08-2021, 01:19 PM   #2
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Check this out. May answer your question. https://sciencing.com/charge-multipl...e-7649425.html
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Old 01-08-2021, 02:38 PM   #3
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When I stored my 5th wheel with dual batteries I used a, if I recall, 5 amp solar charger with the positive lead from the charger to the positive post on battery #1 & the negative lead to the negative post of battery #2, right or wrong?, the batteries maintained 12.3 volts every time I checked them.
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Old 01-08-2021, 03:03 PM   #4
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I have used a Battery Minder for many years. I have two 6V batteries hooked in series on the 5th wheel. Every fall at the end of the season, I hook the battery Minder to them. I've never had to add water, and they stay fully charged and ready to go next spring. Battery Minder states the it keeps your battery desulfated and
charged. I don't remove them from the 5 wheel any more. It has made life just a little easier.

I've got two other ones that I use on my tractor, and my pickup. It doesn't get much use in the winter. I've found with the Battery Minder on the truck, I don't have to worry about the phantom draws killing my battery.

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Old 01-08-2021, 03:55 PM   #5
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Originally Posted by dagst1 View Post
Check this out. May answer your question. https://sciencing.com/charge-multipl...e-7649425.html
Looks good. I will try it. I actually have four 12V batteries, I will hook them up in parallel and trickle charge them and see what happens.

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Old 01-08-2021, 07:41 PM   #6
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Old 01-12-2021, 04:33 PM   #7
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trickle charging your batteries all at once is the best plan. it will keep them all at a exact rate and at the same time.

Because I would in the truck transport industry. I get good used batteries all the time. My ice fishing shack (old 24 ft triple-e trailer) I have 10 type 31 truck batteries in it. I use a progressive dynamic 9200 series charger to charge all 10 at same time. It puts out 50A of charge when they are low and I leave shack plugged in all summer to keep them topped. it puts out 1.5-3.0 amp all summer. This is now the 3rd year on batteries that were supposed to be worn out.

batteries will be perfect in spring with them all connected and trickle charged all winter. Slower the charge= better for battery
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Old 01-14-2021, 04:39 PM   #8
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This is a relatively simple question with a ton of electrical theory behind it.
You charger is capable of outputing 12 Amps MAX, thats why they said to you "Once the batteries are fully charged".

It doesn't matter how many batteries you connect (in parallel + to + and - to -), lets say you are trying to charge 4. As long as the batteries were all approximately full charged the charger would work fine, if however the batteries were almost fully discharged they would exceed the 12 A output and this may destroy the charger. When your car (truck) is charging the battery, after a hard start, the battery may be drawing in excess of 50 A, initially. The RV batteries, if they were almost fully discharged, could be attempting to draw the same (50 A) however we're talking 4 batteries therefore over 200 A. If the charger you are using is designed properly it would shut down, rather than destroying itself due to excessive current draw.

Now since we are trying to "Trickle charge" (or more properly stated, keeping them fully charged) fully charged batteries, meaning the batteries are fully charged when we connect them to the charger, therefore they do not require any charging. Charging a fully charged battery, will ruin the battery due to the constant "boiling of the electrolyte" which will evaporate, and that is BAD.

However a battery sitting around (no charger connected) for 6 months will loose it's charge, we also don't want that either. Thats why we "Trickle charge"

However the charger MUST be designed to actually shut-off when the battery reaches "fully charged" condition, otherwise we are boiling off the electrolyte.

So now let's look at it from the perspective of charging a battery that is NOT fully charged.

When we initially connect the charger, the battery requires a large amount of current (lets say almost 10 A) but as the charge on the battery increases, we want the current draw to the battery, to reduce AUTOMATICALLY, (Taper Off). When the battery reaches full charged condition we want 0.0 A draw, (remember no matter how small the current the result is boiling the electrolyte). Now leaving everything connected over time the battery looses some of its charge, we want the battery charger to recognize that, and AUTOMATICALLY start to recharge the battery to bring the battery charge back up.

No matter whether the batteries are in Series or Parallel these are the steps where the batteries are automatically charged, The problem exists in that we must make the connections to match what the charger output is and what battery configuration we have. Basically RVs run on 12 volts, we can have 2- 6 Volt batteries connected in SERIES, to give us 12 volts, or we can have 2 - 12 volt batteries connected in Parallel to give 12 volts. If you have 4 batteries I suspect that they are all connected in parallel. What about the charger? You state it is 12 volts therefore, your battery connections must equal 12 volts. 4 batteries in parallel = 12 volts,, (matches charger output), 4 batteries in Series = 48 volts (bad for your charger), 2 batteries in Series, which are in Parallel with the other 2 batteries which are also in Series = 24 volts (bad for your charger). Therefore you have 2 choices: connect all batteries in parallel (+ to + and - to -) OR charge each battery separately, that takes away from the automatic charging PAIN IN THE BUTT!

Any charger today worth its cost will be designed to shut off when the batteries are fully charged and AUTOMATICALLY provide a "Trickle" charge to top up the batteries. This includes the "Converter" in all RV units.

Final note any time a battery is charging, one is boiling off electrolyte, the by products of this are Hydrogen (Highly Explosive) and Oxygen (Supports Combustion) therefore only charge batteries in a WELL ventilated area and allow NO Open Flames or ignition sources.

Hope this clears the mud.
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Old 01-14-2021, 06:21 PM   #9
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Egrum hits the nail on the head. I wanted to reply to the thread but just never figured out how would best explain the conundrum. Batteries, charging, charging cycles, voltages, amperage, usage, and conditioning are paramount to proper maintenance. Problematic for general consensus is that none of us utilize the same configurations and therefore no solution will fit all. And that means what works for some will be detrimental for others.
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Old 01-14-2021, 06:56 PM   #10
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The batteries can be left in parallel and charged but only if the batteries are at full charge to start off with a 3 amp trickle will keep them at full with the proper amp hours railroad crossings have a bank of 9 batteries all in parallel and they are constantly being charged only on a 90-day test do we drain all of the power off the batteries
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