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Old 11-02-2019, 02:26 PM   #1
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RE: Battery on Trickle Charger - Removed from RV

I have two new 12 VDC AGM sealed lead acid batteries 75ah (Universal UB12750k) still connected in parallel but removed from RV and placed in house basement with a battery buddy (12VDV, 750ma).

Before connection, battery reading was 12.8VDC. Battery Buddy directions stated device would go into charge mode before switching to stand by once connected. Well 24 hours later it was still in charge mode with batteries reading 13.4VDC.

I disconnected the charging unit, reread directions, nothing mentioned.

Must ask ... Am I doing something wrong? Is this normal?
Or is it because I am trying to maintain or charge two batteries at once?

Any help would be appreciated. Thanks in advance. (see attached pictures)
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Old 11-02-2019, 03:15 PM   #2
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I dont know if it makes any difference, but I do something similar; however, I connect charger's red to one battery and the black to the other similar to the way it's set up in the camper.

I think that charger might be a little weak for the set up. I'm using a 1.25A charger.

Thats my experience. Someone who knows more will help soon, I'm sure.
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Old 11-02-2019, 06:56 PM   #3
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Quote:
Originally Posted by Skip12 View Post
I dont know if it makes any difference, but I do something similar; however, I connect charger's red to one battery and the black to the other similar to the way it's set up in the camper.

I think that charger might be a little weak for the set up. I'm using a 1.25A charger.

Thats my experience. Someone who knows more will help soon, I'm sure.

OK! Thank you!
Might make a difference if I connect positive to one battery and negative to other rather than both on same battery. Nothing to lose by trying.
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Old 11-02-2019, 07:09 PM   #4
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The charger may need to see 13.8V before switching to trickle. See if the manual states when it will switch. May need more time.
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Old 11-02-2019, 08:28 PM   #5
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Quote:
Originally Posted by KEN9XL View Post
I have two new 12 VDC AGM sealed lead acid batteries 75ah (Universal UB12750k) still connected in parallel but removed from RV and placed in house basement with a battery buddy (12VDV, 750ma).

Before connection, battery reading was 12.8VDC. Battery Buddy directions stated device would go into charge mode before switching to stand by once connected. Well 24 hours later it was still in charge mode with batteries reading 13.4VDC.

I disconnected the charging unit, reread directions, nothing mentioned.

Must ask ... Am I doing something wrong? Is this normal?
Or is it because I am trying to maintain or charge two batteries at once?

Any help would be appreciated. Thanks in advance. (see attached pictures)
It's perfectly normal and will depend on the batteries themselves.

Every battery has a small "self discharge rate" which can range on an AGM from 1-2 percent per month on new or good shape battery.

This is for a single battery so if you place two in parallel the amount of discharge (amps, not percentage) will be double.

A small battery maintainer may not have enough capacity to overcome the self discharge rate and make a substantial impact on battery state of charge at the same time.

Battery charging with lead acid type batteries takes a long time to top off so be patient, especially with a small maintainer.

As for how you connect to a pair of batteries at that low a current rate, as long as positive is connected to a positive and negative is connected to a negative that's fine. There's not enough current flowing to worry about different resistances in the paths between batteries as it would be if for example you were running a 2kw inverter.

Hook em back up and give them a week before expecting the charger to switch form Charge mode.
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Old 11-03-2019, 11:44 AM   #6
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Quote:
Originally Posted by Minthillbill View Post
The charger may need to see 13.8V before switching to trickle. See if the manual states when it will switch. May need more time.
Yep! Minthillbill, you are correct. At 13.8VDC after 12 hours the charger finally switched from red (charging mode) to a flashing green which per directions indicates that the battery is at 80%. Guess I just did not wait long enough and was unsure of max voltage for battery.

TitanMike, Thank You! This is the first time I have ever used a trickle charger. Bought an inexpensive one, not knowing what was needed. Always used to remove batteries from TT and place inside basement without any charge. Old stock batteries died, now want to protect or preserve new ones. Probably did not matter how connected as you stated as long as red to red and black to black.

Thank you
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Old 11-03-2019, 11:54 AM   #7
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The max current from that device is very low for two 12V AGM batteries in parallel. It could take long time to get to the trickle stage.
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Old 11-03-2019, 12:25 PM   #8
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The max current from that device is very low for two 12V AGM batteries in parallel. It could take long time to get to the trickle stage.
Flybob, I appreciate the help and input. Thank you!
Guess being new to trickle chargers, I am learning.
Wish I asked questions before purchase so I knew the best charging unit and size to buy.
OK! As long as I know I am doing everything right and have to be patient.
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Old 11-03-2019, 12:56 PM   #9
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During storage months I will usually plug my Battery Tender trickle charger in for a couple of days every month or so.
It typically takes a day or two to top off the charge.
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Old 11-03-2019, 01:08 PM   #10
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If you have a true battery tender you need not keep plugging and unplugging just leave them plugged in they will do what is needed. I been using them on my old cars,campers,lawnmowers never had problems with that.
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Old 11-03-2019, 01:43 PM   #11
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If you have a automotive charger, try charging the pair (in parallel is fine) to full charge *THEN* attach the trickle charger. They were not at full charge and a 0.75amp trickle charger will take forever to get them topped of before going into storage mode.

Plan is sort of like the line from Jaws, the movie.... "we're gonna need a bigger CHARGER..." in your case.

But before spending more money an a new charger, try the topping off with automotive charger first (assuming you have one, or put them back in the trailer and let the converter run for a while to top them off).
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Old 11-03-2019, 01:47 PM   #12
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I have 4-12V AGM batteries that I leave in the camper all winter. No trickle charger, just battery disconnect shut off. Come spring time the batteries are at 12+ volts. Been doing this for 4 winters now. Never found a need to remove the batteries or to put a trickle charger on them.
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Old 11-03-2019, 02:02 PM   #13
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Reaching a certain voltage on a lead acid battery does mean it is fully charged because the batteries have absorption time so it needs to be kept there until absorption takes place. This is often a problem for people who use a charger and make their decision that a battery is charged with their meter. On the bigger solar systems that I have built using 24 L-16 batteries I set the chargers for 2 hours of absorption. These are the chargers built into the inverters, not the solar charge controller.
The one you are using has that built in.
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Old 11-03-2019, 10:26 PM   #14
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You don't need a battery buddy. Your batts were 100% full when you put them on the Buddy. (12.8V)
Disconnected with no Buddy at room temps they will self discarge at about 2% a month meaning that in FIVE months they will STILL be 90% full. This is a huge advantage with AGMs over flooded which discharge at 10% a month in the same conditions.

Just test them individually every few months with a voltmeter to make sure they stay above 12.2V while disconnected. You can even leave them outside and disconnected if you want a SLOWER self discharge in the cold. They will NOT freeze for those 5 months!
That said....point 75 amps at 13.4V ain't gonna hurt a pair of batteries. That is likely the float voltage.
You just don't need it.
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Old 11-03-2019, 11:15 PM   #15
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Quote:
Originally Posted by dward51 View Post
[...] Plan is sort of like the line from Jaws, the movie.... "we're gonna need a bigger CHARGER..." in your case. [...]
If you're going for the Jaws quote, it would be, "You're gonna need a bigger charger."
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Old 11-04-2019, 08:04 AM   #16
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OK! I agree, I should have a bigger charger.
After 48 plus hours or so my battery charger went into stand by mode.
Light is solid green now.

I thank all who offered assistance.

Stay Safe ... Happy Travels
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Old 11-04-2019, 12:13 PM   #17
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Is it safe to connect a trickle charger to a set of battery's still connected to a TT
In cold weather ??? Or is it better to leave TT connect to house power ???
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Old 11-04-2019, 12:41 PM   #18
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.75 amps, I fart better than that, get a noco 3-5amp for maintenance, you'll love it
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Old 11-04-2019, 12:55 PM   #19
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I prefer an intelligent charger that will change charge voltage based on state of charge vs a constant current trickle charger. Two that have have worked well for most members are "Battery Tender" and "CTEK" The CTEK models offer a higher max charge rate and a lithium compatible version. I prefer to not use the onboard convertor as we have lots of line voltage variations due to falling trees. UOTE=Wolverine 1945;2215489]Is it safe to connect a trickle charger to a set of battery's still connected to a TT
In cold weather ??? Or is it better to leave TT connect to house power ???[/QUOTE]
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Old 11-04-2019, 01:08 PM   #20
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I prefer an intelligent charger that will change charge voltage based on state of charge vs a constant current trickle charger. Two that have have worked well for most members are "Battery Tender" and "CTEK" The CTEK models offer a higher max charge rate and a lithium compatible version. I prefer to not use the onboard convertor as we have lots of line voltage variations due to falling trees. UOTE=Wolverine 1945;2215489]Is it safe to connect a trickle charger to a set of battery's still connected to a TT
In cold weather ??? Or is it better to leave TT connect to house power ???
[/QUOTE]

I have a Battery Tender, and was thinking about hooking to two TT, with batters on board, or I could turn on to House Power, from time to time, last winter we had a MN, left it hooked to House Power all winter !!!
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