Dead starting batteries and a high output alternator

[calicamper]

On our boat we have a 80watt solar panel and small two battery solar charger unit.

That would bring your two batteries back up at a nice rate before going big on the Alternator

 

[Photobug]

Web-Land contains alot of battery & alternator myth. Thats become a self propelled load of BS whats become a life of its own.
Btw,
Switching on its headlights will make battery charge faster...

I can see the myths being perpetrated by the web. You can read something, believe it then post it, when someone doubts it link the other expert on the subject.

How does switching on headlights help the battery charge faster?

To the OP consider carrying a jump start battery, they make them big enough to start a diesel.

 

[john61ct]

Was gonna say

good one!

 

[luthj]

Also it's very important to remember that putting a battery on a concrete will cause it to rapidly discharge and die. /sarcasm

 

[Mike W.]

Also it's very important to remember that putting a battery on a concrete will cause it to rapidly discharge and die. /sarcasm

Not if you turn on the headlights first..geez this is exactly how rumors get started..

 

[dwh]

An alternator produces only as much power as is being consumed. It's highly unlikely that a pair of lead-acid batteries could draw enough to max out a 240a alt. No danger to the alt from recharging batteries.

Likewise no danger to the batts being charged by an alt.

The danger is that after running the batts flat, you don't get them back to 100% charged in a timely fashion. Figure 24 hours of engine run time or 12 hours on a decent charger. Minimum.

 

[67cj5]

Run it your not going to hurt the batteries. What I have found with my 7.3 is when I isolated the battery life decreased noticably. Then changing one battery does in the older battery. I always change both batteries when it's time.I have owned my F350 since new 2001. It's got 450,000 on it and it still runs fine. 7 sets of batteries and 3 alternators in that time. One tremendous motor..

Some thing else is going on there for you to need 7 sets of batteries and 3 alternators, That's 2 and a half years per set of batteries,

 

[NatersXJ6]

Some thing else is going on there for you to need 7 sets of batteries and 3 alternators, That's 2 and a half years per set of batteries,

I’m guessing crappy batteries combined with hot weather. My F250 burns batteries up at about the same rate, maybe a little faster. If the OP lives in a place where dead batteries in Death Valley are a true concern, than he probably (like me) lives in a place where ambient temperatures routinely climb over 100 F. Officially, we had 47 days over 100 so far this year, realistically, I think it was probably closer to 60 days. Even if you meticulously maintain water levels, cheap starting batteries under hood with a big diesel don’t last long. Expensive ones don’t either, so I stick with cheap and replace often.

 

[luthj]

High Ambient temps (sustained) reduce battery life.

The optimum operating temperature for the lead-acid battery is 25°C (77°F). ... VRLA, which would last for 10 years at 25°C (77°F), will only be good for 5 years if operated at 33°C (95°F). Theoretically the same battery would endure a little more than one year at a desert temperature of 42°C (107°F).

https://prod-ng.sandia.gov/techlib-noauth/access-control.cgi/2004/043149.pdf

 

[verdesard0g]

In my dodge CTD cheap Walmart batteries last about 5 years here in central AZ. Temps over 100 just about every day in summer. Always replaced in pairs. An isolator for two starting batteries in a diesel???
Dumb idea if you ask me.

 

[67cj5]

Thanks Guys for chipping with a response, Because I had a Mitsubishi 2.5 TD SUV and it came factory fitted with Twin Batteries, It only had about 70,000 on the Clock when I got it and the first thing I did was replace the batteries and Oil etc as you Do when you get another vehicle, But a year later the batteries died, So again I bought another set of 85Ah Batteries only this time I sat a 15w solar panel on the dash and hooked it up to the main battery, Again they lost power, It did have a very small parasitic drain caused by the Alarm system but not enough to drain both batteries in about 6 weeks But sure enough within 3 weeks the batteries were flat,

This got me thinking that the factory Duel Battery charging system is either very Lazy or badly setup I think the Alternator was around the 85/90Ah mark, When you started it you would hear the solenoid click and then it would click back possibly changing from one battery to the other, But not once did I hear them changing/clicking when the vehicle was going down the road,

This makes me think that the system they use is not a proper Duel battery system, meaning it clicks over to the 2nd battery to start and then goes back to number 1 once it is running and then it only charges either battery once its voltage gets below a certain point at rest I checked the batteries and it was quite common to see both of them around the 12.4 to 12.6v mark which tells me that these systems are not set up to keep Duel batteries at their peak, Which brings back to whats going on with this powerstroke/7.3 or what ever it's called, because a good battery should be able to start the 2.5 I had or a 7.3,

I think it might pay in the long run to ditch the factory Duel system and fit an after market system that is designed to keep both batteries at their peak, My newer Shogun still has the 2.5 TDI in it and only a single battery setup but I will change all that at some point, But factory Duel systems just don't manage the power like an Off Road systems does.

 

[Ducky's Dad]

To the OP: I had several pairs of Optimas in my GMC gasser and several times had to charge them from dead with a puny, stock 105amp GM alternator. No damage.

I have had that truck for over 20 years and always ran Odyssey or Optima AGMs in it, always in pairs. Last year I needed fresh batteries on short notice and all I could find quickly in the right size was a pair of Deka FLAs, so that's what I bought. Price was right on the Dekas, but they have noticeably less capacity than the AGMs. Obvious when the truck sits for a week with the alarm armed.

 

[ducktapeguy]

I admit I have used my alternator to charge my dead car batteries many times, but the last time I took an alternator to a rebuilder (an actual old school rebuilder and not just swapping for rebuilt) he told me that was the worst thing I could be doing. The internal wiring in most vehicles alternators aren’t rated to handle high current for prolonged periods, they’re meant to top off a nearly full battery and keep the electronics running, so eventually you’ll burn it up. I would assume two dead batteries would make it even worse. In an emergency situation I’d probably still do it and risk damaging it, but I’d keep an eye on the alternator temps and probably let it cool every so often. Now I’ve invested in a decent battery charger for home use and I haven’t needed to replace an alternator in a while

Also there are some alternator rated for continuous duty cycle (leech Neville/prestolite), but those are significant larger and heavier than what you find in most engine compartments. I have a 140 amp one that came off a semi truck and it’s about twice as large and twice as heavy as a standard alternator

 

[luthj]

I hear a lot of references to "burning things up". Maybe 30 years ago; but It just doesn't happen often anymore. Maybe with the tiny undersized electrical systems of the 70s, but most vehicles come with 130A+ alternators stock, and well designed electrical systems.

Plus lead batteries simply won't accept charge rates over 0.5C for more than 20-30 minutes before they start to taper off rapidly.

 

[john61ct]

I admit I have used my alternator to charge my dead car batteries many times, but the last time I took an alternator to a rebuilder (an actual old school rebuilder and not just swapping for rebuilt) he told me that was the worst thing I could be doing.

Yes he is wrong, no problem for the alt doing this.

Much better for **the battery** though to be put on an intelligent mains charger in order to get it recharged to Full overnight.

But if you plan to drive say 15 hours in the next couple days, that wohld be fine too