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Old 04-20-2019, 10:13 AM   #1
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Charge Both Starting Batteries connected in Parallel or each separately?

Have two Duracell Ultra SLI31SA Group 31 Heavy Duty Fleet Batteries connected in Parallel (last year new). I didn't have a battery tender and had been using a multi-state charge every two months to charge them to 100% (while connected in Parallel).

Of course the parasitic battery drain has been constant while sitting and I went 5 months or so without a charger so the batteries read 11.89v.

Right now, I have the multi-stage charger on them but I am curious.

Since they are depleted, would it be best to charge each battery to 100% separately (batteries not connected together)?

I am going to buy a decent battery tender and I think I will go with a BatteryMINDer® Plus Charger Model 12117: 12V 1.33 AMP Charger-Maintainer-Desulfator which is sold exclusively at NorthernTool and is on sale for $25:
https://www.northerntool.com/shop/to...2201_200332201

I noticed in the description:
Quote:
8-stage unit charges and maintains from 1 to 4 batteries at a time (12V batteries parallel-connected or two 6V batteries series-connected. NOTE: Never connect 2 or more batteries together in parallel before fully charging each and checking their condition. Failure to fully charge each battery and check their condition can result in a serious safety hazard)
I just put the battery charger on them about an hour ago. Now I am thinking I may want to disconnect them and take the time to charge each battery separately.

How have you charged two discharged batteries connected in parallel?


The BatteryMINDer units have the ability to desulfate batteries if needed.

.
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Old 04-20-2019, 10:33 AM   #2
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If you have the electric access, leave them together. It may take twice as long, but not longer then doing each, one at a time.

The caution about not connecting them together is if they weren't. Since they are, they are equally discharged, just like one large battery.
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Old 04-20-2019, 10:51 AM   #3
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Thank you @twinboat - I'll keep the charger on them as is (parallel connection).

So after reading the specs on that Northern Tool exclusive model, it's float/maintenance current is only 5mA - 200mA.

The next model up, BatteryMINDer Model 1510, has a maintenance current of 0 - 1.5A.

I don't think 200mA will keep up with the parasitic drain. Has anyone measured their drain?

I'm not sure if BatteryMINDer's Patented Desulfator technology is needed.


Any battery tender model recommendations for these heavy duty truck batteries?


.
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Old 04-20-2019, 10:59 AM   #4
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If I had parallel batteries that were discharged, and I was using a multi-stage battery charger, I would charge them individually.


Lead acid batteries actually last longer if you do not leave them on a continuous battery maintainer. After the are fully charged from the first step, plug your maintainer into a cheap mechanical lamp timer and only charge them a few hours a day.
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Old 04-20-2019, 11:03 AM   #5
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Quote:
Originally Posted by CoachStreamr View Post
Have two Duracell Ultra SLI31SA Group 31 Heavy Duty Fleet Batteries connected in Parallel (last year new). I didn't have a battery tender and had been using a multi-state charge every two months to charge them to 100% (while connected in Parallel).

Of course the parasitic battery drain has been constant while sitting and I went 5 months or so without a charger so the batteries read 11.89v.

Right now, I have the multi-stage charger on them but I am curious.

Since they are depleted, would it be best to charge each battery to 100% separately (batteries not connected together)?

I am going to buy a decent battery tender and I think I will go with a BatteryMINDer® Plus Charger Model 12117: 12V 1.33 AMP Charger-Maintainer-Desulfator which is sold exclusively at NorthernTool and is on sale for $25:
https://www.northerntool.com/shop/to...2201_200332201

I noticed in the description:
I just put the battery charger on them about an hour ago. Now I am thinking I may want to disconnect them and take the time to charge each battery separately.

How have you charged two discharged batteries connected in parallel?
Happens every time someone fires up their motorhome after it's been sitting for a while, if they have 2 coach batteries connected in parallel, and both are depleted from parasitic draw. Probably the easiest way to do it. Assuming you have a newer coach with at least a 3 stage charger. How well it works will depend on what kind of shape the depleted batteries are in.

Quote:
Originally Posted by CoachStreamr View Post
The BatteryMINDer units have the ability to desulfate batteries if needed.

.
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Old 04-20-2019, 11:19 AM   #6
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Quote:
Originally Posted by Winterbagoal View Post
Assuming you have a newer coach with at least a 3 stage charger. How well it works will depend on what kind of shape the depleted batteries are in.
It's a '96

My Coach's charger doesn't touch the Chassis Batteries, it only charges on House/Coach batteries and is the reason why I have been putting the charger on there every 1-2 months except the last 5 months

I want to put on a decent battery tender. I never measured the current draw, I have a feeling it's over 200mA and not sure that one model will do the job.


Quote:
Originally Posted by theoldwizard View Post
Lead acid batteries actually last longer if you do not leave them on a continuous battery maintainer. After the are fully charged from the first step, plug your maintainer into a cheap mechanical lamp timer and only charge them a few hours a day.
I didn't know that, I thought that was the whole point of a battery tender.


If anyone has measured their Coach's parasitic drain, what was the reading?


.
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Old 04-20-2019, 04:04 PM   #7
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I was answering your (what I thought was a) rhetorical question, "How have you charged two discharged batteries connected in parallel?", by saying it happens all the time in the real world, when a coach has 2 or more batteries connected in parallel, on a newer charger, every time they fire up the chassis engine, or generator if they have one. I thought you were concerned that there was something special about recharging them while they were connected in parallel, versus separated, prior to recharging.

Sorry, if this, or my other answer, was confusing. I know it wouldn't be the first time.
I think my parasitic drain on my coach batteries is primarily the inverter itself (which is on all the time), the monitor panel, the alarm system, and maybe the CO and Propane detectors which work off 12VDC. The total draw under that load might be a tenth of an amp, give or take? I've seen that much being sent to the batteries on a sunny day from my 3X100W panels, by my solar charge controller, when I know the batteries are full. So I assume it's trying to offset the parasitic draw to keep them full at that rate.
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Old 04-25-2019, 03:45 PM   #8
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Quote:
Originally Posted by CoachStreamr View Post
Any battery tender model recommendations for these heavy duty truck batteries?
I decided to order the BatteryMINDer Plus Charger/Maintainer/Desulfator — 1 Amp, 12 Volt, Model# 12117TC, Exclusive sold by Northern Tool.

https://www.northerntool.com/shop/to...2201_200332201

I spoke to VDC Electronics's (BatteryMINDer) technical support and this is actually a new model, released in Nov/Dec 2018.

It has the same 8 stages and Temperature Compensation like the BatteryMINDer 1510 and is only $25 - 1 Amp vs 1.5 Amp.

The 12117TC replaces the much older design 3 stage 12117.

It takes the same accessories as the 1510. I will be ordering the ABS-248 At the Battery Temperature Sensor since the charger/minder will be in a separate bay from the Chassis Battery bay.

.
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Old 04-26-2019, 05:22 AM   #9
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if having draw. start the gennie for an hour or so each month. thats good time to excercise and charge.
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Old 04-26-2019, 06:59 AM   #10
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The only negative is.

If one battery has a dead or shorted cell. ?

So if they are NOT taking a charge like they should ?
Disconect and test separately.

Charging separately will also tell you the bad battery.
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Old 04-26-2019, 11:21 AM   #11
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Voltage across both went down to 11.89v. If I think there is an issue, I would do each individually. The 8 stage charger can also indicate if there is an issue (like bad cell), though I'd have to then test each separately to see which one.

My local Interstate Battery location will test any battery, including over a few days and regardless of brand - at no charge. I actually had brought the House batteries to them (two Costco Golf Cart 6v) and they brought them back, had them on their unit for 4 days. One of the connectors on them was bad/cracked and wasn't making connection all the time (especially when we were in the Coach), causing the Coach charger to be disabled and batteries draining (after we first bought the Coach). Interstate's main tech came out to the house and replaced all battery heavy duty connectors and heat shrink (both Coach and House banks) - only charged $60.

My bench 2/10amp multi-stage charger brought them back up (about 3 days) and has them now in maintenance mode. The new maintainer will be here next week. I kept them connected in parallel and in the Coach.


Quote:
Originally Posted by theoldwizard View Post
Lead acid batteries actually last longer if you do not leave them on a continuous battery maintainer. After the are fully charged from the first step, plug your maintainer into a cheap mechanical lamp timer and only charge them a few hours a day.
I asked their Tech Support about this as well an he thought that this would be a good idea (for those starting batteries while the Coach is sitting) though that BatteryMINDer 12117TC can be used full-time. He did say that with the BatteryMINDer I got, it would be best to let it be on for 2-3 days straight (once plugged in, that model can take a day+ for it to go into float/maintenance) then off. I am thinking having it on or 3 days each week at first. Perhaps 3 days every 2 weeks, I'll check voltage several times and see how it goes.

So, is there a timer switch that can select so days in a week can be selected/turned off vs hours in a day?


Here are the 7 Stages from the 1510, not sure what the 8th Stage is on the new 12117TC:
Quote:
The Seven Stage Charging Process:

Analyze - Test-Qualify/Accept or Reject battery
Desulfate - Begins removal by dissolving harmful sulfate
Soft Start - Applies low current if battery tests low
Bulk* - Provides maximum output to charge to 85%
Absorption* - Provides low current to complete to 100%
Test - To determine if battery needs further desulfation
Maintenance - Maintains temperature-compensated full-charge
.
Quote:
These models come equipped with sensors for Automatic Temperature Compensation (ATC) from 0°F to 130°F. These sensors are either Ambient (ATS) already installed or the optional At-the-Battery (ABS-248) depending on the model. This ensures 100% charge without ever over- or under- charging. The sensor accomplishes this by sending electrical information to charger so it will know when to lower its voltage (warm-hot) or raise voltage (cool-cold). The purpose of the optional ABS-248 sensors is to detect temperature at and within the battery itself rather than the temperature surrounding it or the charger. This is very important if charger is not close to (in same ambient atmosphere-temperature) as the battery. Proper temperature compensation significantly increases battery life. Any charging device that is not equipped with accurate temperature sensing should never be used in temperatures above 80°F and below 60°F, especially when being maintained for weeks-months at a time. If used expect battery life to be significantly shorter with poorer performance during its shortened life as well.


*All BatteryMINDer® models provide 100% full-time variable frequency pulse type desulfation** automatically (no buttons to push).
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Old 04-27-2019, 03:23 PM   #12
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Originally Posted by consolenut View Post
if having draw. start the gennie for an hour or so each month. thats good time to excercise and charge.
On this Coach, it doesn't look like the generator charges the Start/Chassis batteries (unless the system knows the batteries are at 100%. I exercised the generator today and read the voltage on those batteries: 12.82v, same when not running the generator and the batteries are fully charged.

.
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Old 04-27-2019, 03:32 PM   #13
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Originally Posted by CoachStreamr View Post
On this Coach, it doesn't look like the generator charges the Start/Chassis batteries (unless the system knows the batteries are at 100%. I exercised the generator today and read the voltage on those batteries: 12.82v, same when not running the generator and the batteries are fully charged.

.
12.8 is higher then most battery resting voltage.

Were you plugged into shore power before you started the generator ?
The generator runs the same charger as shore power and if the batteries are at 100%, it may maintain 12.8 volts.

Resting voltage of most batteries is between 12.6 and 12.7 volts.
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Old 04-27-2019, 03:42 PM   #14
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I used a cheap Harbor Freight multi-meter, got 2-3 of them for free. Not sure how accurate those are.

My bench charger was connected to the Start Batteries (I measured 12.81 - 12.82 while still connected) and the light indicated the batteries were fully charged so was in maintenance mode.

Before starting the generator today, I unplugged the bench charger from A/C and the batteries, started the generator and after about a minute disconnected shore power. Turned the 1200 watt heater on and a fan for load.

I still read 12.82v on the Start Batteries. Checked a few times while I ran the generator for about 20 minutes.

I know for a fact that the Start/Chassis Batteries do not get charged while on Shore Power with this Coach.

.
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