Battery maintainer in vehicles with dual batteries

[SC Maintenance]

Thing is you have parasitic losses in the cables as well as the batteries. They don't convert 100% of the incoming current to charge. There is loss there as well.

I was incorrect with one thing. I thought I remembered Noco putting a limit on the charger:

View attachment 251320

Looks like that is just for charging, maintaining they seem to think it would be ok. Still, with temps dropping he's probably better off with a bit bigger unit.

I am also not taking my own advice. I have a Genius1 in the garage on a Marine battery and a backup group 35 in parallel. Although there's nothing hooked to them, the cables are short, etc. Plus they're not mission critical, I'm not depending on them to crank anything.

Bigger is always better

There is also a duty cycle they likely don't publish - but its unlikely a 1A Noco would be allowed to push 1A continuous. Probably throttles back based on internal heat.

Still, the truck is parked and not used, and once asleep shouldn't pull more than 100mA, probably much less, plus the parasitic drain of the battery in general. I don't think not enough Amps is his problem in this case.

 

[dnewton3]

Some misinformation going on here ...

I am assuming this is a motor-home, given it's an F350 chassis.
- it is true that the chassis battery (for the vehicle) will always be "connected" to the vehicle; this is the one that needs charging for successful starts
- the house battery (for the RV portion) is charged by the system, but it should be isolated when the engine is not running
You need to make sure which one the charger is on; it is likely that the owner's manual describes which is which
You can, if you want, connect a smart charger to each one and in fact it would not be a bad idea, (assuming the isolation circuit is functioning properly.) Just make sure the engine is off when you connect both chargers, and make sure they are both disconnected before starting the vehicle.


The following won't apply to GON's application, but I want to clear up some info ...
As for true "dual" battery systems (such as a typical light-duty diesel truck), these run the batteries in parallel, and are connect at all times to the vehicle system. The preferred way to use a smart charger on these is to put the "+" on one battery and the "-" on the other battery; this way it charges them as a set and the voltage will be equal between the two (it negates any voltage drop in the cables between the two batteries). I did this on my 2006 Dmax and never had one problem with the OE batteries for the 12 years I owned it.
Read this FAQ; skip down to figure 9 and read the associated details just under that image.
https://www.batterytender.com/pages/series-parallel


There are many brands of smart chargers. I am loyal to Battery Tender because of the successes I've had with this brand. But I do agree there are other good brands out there. The important thing to realize is that each of these brands has a FAQ section; pretty much any question you have would be answered by seeking the info therein.

 

[wwillson]

@GON

See this post I made on the RV site about charging multiple batteries with one charger.

https://rvthe.us/community/threads/...i-have-a-bad-or-shorted-battery.422/post-2435

 

[GON]

@GON

See this post I made on the RV site about charging multiple batteries with one charger.

https://rvthe.us/community/threads/...i-have-a-bad-or-shorted-battery.422/post-2435

Really helpful , thanks for the link. I suspect this may in fact be the issue and I need to pull the ground from one of the batteries and have two battery maintainers hooked up.

 

[eljefino]

The batteries will be interconnected with huge cables capable of starting the truck with hundreds of amps. Feeding one amp, or 0.5 amps, through those cables will encounter ridiculously low resistance and they won't be a factor, so long as the terminals are clean. The truck charges them with it's 100-something amp alternator through the same wiring.

The best paralleled batteries are installed at the same time, with the same size, manufacturer, lot number, etc.

However, when they get old, it is handy to "recondition" them on a more granular basis, so disconnecting one and giving it its own trickle charger will improve the situation for both batteries. If we could disassemble them and charge each two-volt cell individually, that would help even more.

But I think the truck shut down its accessories after two weeks like mentioned above, to save batteries. Many vehicles ship with missing fuses that the delivering dealer installs, to wake up the comfort accessories. Or that stuff kicks on after 25 miles hit the odometer.

I have a Noco Genius 1 amp charger, and I brought my kid's Camry group 35? battery back from 20% SOC in two days, so I think they do ok under long continuous usage. It was an ambient temp of ~45'F if that matters.

 

[wwillson]

The best paralleled batteries are installed at the same time, with the same size, manufacturer, lot number, etc.

Identical batteries can still have different internal resistance, which makes them very difficult to charge with a single charger. The best way and sometimes only way to maintain multiple batteries is to disconnect them and maintain them with their own maintainer.

 

[SC Maintenance]

Identical batteries can still have different internal resistance, which makes them very difficult to charge with a single charger. The best way and sometimes only way to maintain multiple batteries is to disconnect them and maintain them with their own maintainer.

I assume this is because in a parrallel circuit the current varies / voltage is the same. So even if he had the - on one battery and the + in another - the majority of the current would flow through the battery with the lowest resistance - for example?

 

[Jetronic]

Unless Ford included some sort of isolation so one doesn't drain the other if one goes dead?

that's the easiest thing to measure and/or defeat

 

[Jetronic]

Really helpful , thanks for the link. I suspect this may in fact be the issue and I need to pull the ground from one of the batteries and have two battery maintainers hooked up.

But you never said it's an RV. Cars and trucks sometimes have 2 12V batteries ti increase the total amperage, it's not a starter and accesories battery. RV are different bof course.

 

[Jetronic]

I assume this is because in a parrallel circuit the current varies / voltage is the same. So even if he had the - on one battery and the + in another - the majority of the current would flow through the battery with the lowest resistance - for example?

View attachment 251322

No, you need to put the voltage sources from the batteries in there too. The current will split but most will flow to the battery with the lowest voltage.

 

[wpod]

This may be off topic but the wife had a 2002 F250 with the 7.3 Power stroke engine and like clock work one of the batteries would die and the other one boil out. I replaced the batteries about every two and a half years. I would at the time buy Costco and return them, The original batteries did the same thing.

 

[eljefino]

No, you need to put the voltage sources from the batteries in there too. The current will split but most will flow to the battery with the lowest voltage.

Yup, this... the resistance batteries face charging sources with varies with state-of-charge. So when one battery "fills up" the next one with lower resistance will keep taking current until it, too, fills up then the assembly presents the charger with a higher resistance and current flow drops.

Ideally the two batteries match charging profiles, but as several posters mention, an exclusive charge for each one may be beneficial now and again.

 

[Pelican]

The Ford app sent me a message that my 2919 F350 with dual batteries is turning off its Internet monitoring program due to low battery voltage.

The F350 has been parked for a month. A smart battery maintainer is hooked up to one of the two batteries.

So, I am guessing either the battery maintainer has become unplugged or failed, or that the battery maintainer only charges the battery that the maintainer is connected to,- not both batteries. And the battery that powers the Internet monitoring of the vehicle is not the battery with the maintainer connected.

Am I missing anything in my analysis of the situation?

The maintainer ONLY charges the battery it's connected to. I'm assuming that the 2nd battery is a 6v like a Yuasa that controls the electronics (like MB used to have) The latter is charged by the alternator (same as the main one) but a maintainer is not connected to the alternator that's why the 6v is not charged. You need to charge it separately.

 

[RhondaHonda]

It’s an F-350 truck with 2 big batteries, like they’ve been doing for years. Hopefully that clears everyone up on what is taking place here.

 

[ctechbob]

The preferred way to use a smart charger on these is to put the "+" on one battery and the "-" on the other battery; this way it charges them as a set and the voltage will be equal between the two (it negates any voltage drop in the cables between the two batteries).

You'd have thought I would have remembered to mention that since I just got done with that solar install and did the same thing there.

He's 100% correct, positive on one battery and negative on the other.

 

[eljefino]

It’s an F-350 truck with 2 big batteries, like they’ve been doing for years. Hopefully that clears everyone up on what is taking place here.

It doesn't because it could be a cab-and-chassis used for an ambulance or RV which will have separated systems. That's why we've been asking questions to narrow things down.

 

[f355spider]

On my BMW there are two batteries, but they are isolated so must be charged individually.
Battery Minder brand battery tenders can charge multiple batteries, and offer this device to make it easy to connect them up:
https://www.batteryminders.com/multiple-battery-connector-210-AY

The Battery Minder I have has 2, 4, 8 amp settings. The recommend using the 4 amp setting for 2 or more batteries.

 

[ctechbob]

It doesn't because it could be a cab-and-chassis used for an ambulance or RV which will have separated systems. That's why we've been asking questions to narrow things down.

It's not, it is the F350 he rebuilt a while back. Just a regular ol F350.

 

[GON]

My RV had a house battery and a starting battery, both underhood, with the house battery isolated with the key off. But if you have, say, a diesel, you'll have them both paralleled, and both will charge off that little wall wart.

I assume the vehicle is some distance from you, and hard to check on?

Yes, the vehicle is about 8,000 air miles away

 

[JHZR2]

One amp isn't enough for two big diesel batts. Probably need at least a 5 amp charger for that. I know Noco doesn't recommend their 1 amp charger for full sized car batts (Even though it does work).

But yes, those batteries are just connected in parallel. Only need to connect to one of them, although there will be a (very) slight voltage loss across the cables, it should be negligible.

I’ve used the Noco 1A and 2A units for my dual group 27 batteries.

OP, there’s no issue there. Both batteries will charge. Losses in the conductors may result in one being slightly less charged than the other, but it shouldn’t much matter. I suspect it was just the batteries’ time. Especially if they have continuous draws even with the vehicle off.

That said, you should be able to probe the batteries and conductors to verify resistances from point to point.