Looking to maintain the batteries....

[Dajain]

Good Morning Everyone!
I have a 1999 Freightliner which I use as my travel rig and the batteries in the truck are four, 31 series commercial batteries hooked up in parallel for a 12 volt system.
But, here is the problem....I use the truck maybe 5 times a year and with the lack of use, I have to charge the batteries every time I go to use it. This results in shortened lifespan of the batteries, about 2 years on the last one that went bad.
What I am looking to do is have enough solar power just to maintain these 4 batteries. I have a small solar panel mounted to the roof (maybe 50 watt?) and I still have to charge it every time.

Here are what I have tried:
-pulling the 2 fuses for the house systems to remove any drains.
-Disconnect the negatives from the frame
-the current solar panel with controller

The batteries still need to be charged each time.
What I haven't done:
-disconnect all batteries from each other
-checked for drains on main circuit

One thought I have is I have a rotation of batteries going bad which keeps draining the rest while resting, so here is my question....

I am planning on just replacing all 4 batteries at once (probably tomorrow) to eliminate the rotating door of bad batteries, but what size solar system would I need to just maintain a charge on these 4 commercial batteries?

Battery info:

https://www.napaonline.com/en/p/BAT7236

Thanks for any info!

 

[Mark_K5LXP]

1% of Ah rating is enough to keep up with self discharge. So a nominal 10W panel would be enough for a 100Ah battery. Here's the "but" - in winter, net solar is down 50% over summer, so you need 2X that. Another "but" - you don't know what your drains are. This formula only works if the batteries are the only load. It also affects their net life because even if solar is replenishing them every day, they're discharging every night and that's accelerating their demise to some extent. So your effort is twofold - solar supplement and drain mitigation.

Mark B.
Albuquerque, NM

 

[Dajain]

I 100% agree that there is more than one factor and want to address the added concerns.

Wintertime sun is definitely less than summer sun. I am in Southern Utah, so it goes without saying that my winter sun is better than Northern states. If I remember right, we see almost 5 hours in the dead of winter. This alone should be plenty to maintain according to the marbles I have rolling around.

Drains... Yes, I'm sure this is my main issue. Whether it's from a bad battery draining the rest, the stereo memory wire, or even the ECM constant power. It is my goal to get to the point where there are no drains on the batteries, even if that means putting main disconnects in the system.

So my thinking was originally correct, right? This 50 watt panel would be enough to maintain if the batteries are charged and in good condition with no external drains...

 

[OldWEB]

My question is why is their a requirement for four 12V batteries if this is just (to start) the travel rig? Is this bank also used for the RV 'house' batteries?
But just changing out one failed battery in a group of four is a no-no... the next older battery will suck out the life of the remaining ones. Change out the whole group (if you need four) and check that all are of the same manufacture date also.

 

[OldWEB]

And you should disconnect completely one terminal from each battery to ensure no drain... even between the next battery. Then before reconnecting the bank, check each batteries voltage level for early diagnostic information, they should easily last a year before a recharge. I do 6 months through a freezing winter with only a drop to 12.4VDC.

 

[rvlifer]

do you have a battery monitor installed? If you are gonna keep the batteries connected you are just guessing what is going on without one.

If you want to use aolar to keep them charged you will need more than you think to compensate for the times they arent producing power.

 

[Dajain]

My question is why is their a requirement for four 12V batteries if this is just (to start) the travel rig? Is this bank also used for the RV 'house' batteries?
But just changing out one failed battery in a group of four is a no-no... the next older battery will suck out the life of the remaining ones. Change out the whole group (if you need four) and check that all are of the same manufacture date also.

4 is what the truck came with originally and that is what the battery tray holds. Even if the starter takes 2k amps to start the cold motor, there is still plenty of reserve.
When I replaced the 2 last time, my tester (Solar brand, not Harbor Freight, haha) said the other 2 were good. It would get pretty pricey, pretty quick if 4 batteries were replaced every time one went bad.

I tested all 4 batteries today and 3 tested weak. All 4 are getting replaced tomorrow.

 

[Dajain]

do you have a battery monitor installed? If you are gonna keep the batteries connected you are just guessing what is going on without one.

If you want to use aolar to keep them charged you will need more than you think to compensate for the times they arent producing power.

My inverter has a low power warning on it, but that only works when I have it on. And besides, when the batteries are connected in parallel, a monitor would read the voltage on all the batteries together. wouldn't be very accurate unless the batteries can be isolated while in use to monitor each battery.

 

[Dajain]

Tested my main battery lines and there is a 1 amp draw from somewhere in the truck, sooo....

What I did today was went thru the battery bank and wiring. I installed 2 disconnects for the smaller loads (ECM (+) and inverter (-) and that leaves only the negative cable to the starter to disconnect when she is parked. This will completely isolate the batteries from the truck while parked.

I'll also make it so the solar system is hooked up 100% of the time no matter what else is shut off and disconnected and this should produce a trickle charge to keep them topped off hopefully.

With the batteries disconnected and a trickle going, we'll see if this is enough to keep the batteries healthy.

 

[rvlifer]

My inverter has a low power warning on it, but that only works when I have it on. And besides, when the batteries are connected in parallel, a monitor would read the voltage on all the batteries together. wouldn't be very accurate unless the batteries can be isolated while in use to monitor each battery.

A good battery monitor is far more than a voltage meter. Suggest you install a good one. It will calculate accurate soc and help you understand if something is drawing power unexpectedly.

 

[Dajain]

A good battery monitor is far more than a voltage meter. Suggest you install a good one. It will calculate accurate soc and help you understand if something is drawing power unexpectedly.

I do understand a good monitor does more than just voltage, but when you have 4 of these big boys in parallel, you're talking 1680 amp hours in reserve when the batteries are in good condition and fully charged. If something does a fast amperage drain on these, there would be smoke/fire before the monitor could save ya. We are talking about a lot of reserve with these.

Considering I use the truck maybe 5 time a year, the bigger concern is long term battery conditioning than monitoring during use. I don't do long term use without driving during the day.

This doesn't mean I won't look into a decent monitor. Looking at the monitor would be a lot easier than disconnecting and testing each battery.

 

[rvlifer]

I do understand a good monitor does more than just voltage, but when you have 4 of these big boys in parallel, you're talking 1680 amp hours in reserve when the batteries are in good condition and fully charged. If something does a fast amperage drain on these, there would be smoke/fire before the monitor could save ya. We are talking about a lot of reserve with these.

Considering I use the truck maybe 5 time a year, the bigger concern is long term battery conditioning than monitoring during use. I don't do long term use without driving during the day.

This doesn't mean I won't look into a decent monitor. Looking at the monitor would be a lot easier than disconnecting and testing each battery.

It is a monitor, not an alarm. My trimetric on an 8 battery bank does what it is supposed to do. It tells me where my battery bank is in regards to soc and how much power is being added or removed so i have the info i need to manage them properly.

you will still want to disconnect your batteries for long term storage.

 

[Dajain]

It is a monitor, not an alarm. My trimetric on an 8 battery bank does what it is supposed to do. It tells me where my battery bank is in regards to soc and how much power is being added or removed so i have the info i need to manage them properly.

you will still want to disconnect your batteries for long term storage.

You obviously use your system more than 5 overnight trips per year and I'm sure the system you have works awesome. The simple fact is, the truck sits dormant most of the year and I'm just wanting some input as to what will be needed to keep the batteries healthy during the dormancy for months of the year.

Since I have modified the truck/battery system to completely isolate the batteries while in storage, now is back to the original question. What is needed from a solar system to keep my batteries charged, healthy and ready to go when I need them? All the external drains are removed.

Wouldn't a battery monitor system add an external drain during these long dormant periods?

 

[rvlifer]

You obviously use your system more than 5 overnight trips per year and I'm sure the system you have works awesome. The simple fact is, the truck sits dormant most of the year and I'm just wanting some input as to what will be needed to keep the batteries healthy during the dormancy for months of the year.

Since I have modified the truck/battery system to completely isolate the batteries while in storage, now is back to the original question. What is needed from a solar system to keep my batteries charged, healthy and ready to go when I need them? All the external drains are removed.

Wouldn't a battery monitor system add an external drain during these long dormant periods?

Without knowing your drain and what is causing it how much solar you need would be nothing more than a guess. The battery monitor provides that info.

Most people say if they disconnect their batteries they dont need to worry about charging them at all for up to 6 months but every situation is different.

I think you said you were considering a 50 watt panel? My portable 100w panel puts about 6 1/2 amps into the batteries in full sun. My 2000w rooftop setup provides about 75 amps in full sunlight.

If you know what the draw on the battery is that should be enough to make an educated guess at what you need. Disconnecting the battery will reduce how much solar you need but doesnt tell you what is drawing power when it is connected. Personally i would like to know that so i can manage the batteries regardless of whether i am using the rv so the bmk is very useful

Here is info about the trimetric i have. It should help you decide if it will help you in this situation. I am sure there is a small draw from the trimetric but i dont know how much. I cant imagine it is very large or would have an impact on keeping the batteries charged.

https://www.bogartengineering.com/products/battery-monitor.html

I am not familiar with your setup to say whether you need one or not to do what you are trying to do. If the 4 batteries are your house batteries i suspect it will help a lot. If they are your chassis batts then maybe not.

 

[rvlifer]

And fyi that that 6 1/2 on the portable is what the charge controller is sending to the batteries. The rooftop number is from my bmk so is what is actually getting to the battery. There will be a slight voltage drop from the solar to the batteries so if you are trying to be as accurate as possible factor that in

 

[Dajain]

I am not familiar with your setup to say whether you need one or not to do what you are trying to do. If the 4 batteries are your house batteries i suspect it will help a lot. If they are your chassis batts then maybe not.

My set up is a 1999 Freightliner FLD120 sleeper cab which came standard with the 4 battery configuration it had from the factory.

The 4 battery configuration is the chassis and house system. There is no separation between the 2 systems. In the sleeper, I have a 3000 watt inverter, a 13" flat screen TV with a built in DVD player, 1100 watt microwave, 2 LED lights, a NAPA 12 volt fan, a single cup Keurig coffee maker and just recently installed a diesel heater.

When I use the truck, the most common scenario is this:
-Start the truck up and let it build air and warm up a little. Usually 30 minutes.
-Drive the truck an hour away (Hwy speeds) to the destination
-Heat my dinner in the microwave
-Do what I need to do outside, heat my dinner in the microwave, then relax with a movie before bed
-Shut off the inverter at night
-Wake up in the morning and start the truck to warm it up
-Turn on the inverter
-Microwave my breakfast and make a cup of coffee (main engine is still running)
-Finish breakfast and drive home the 1 hour at hwy speeds
Then the truck sits until the next time I need it, which could be a couple weeks or 9+ months.

The longest I've used the truck was from Utah to North Carolina. Only thing that changed on that trip was the length of time driving. Instead of 1 hour, it was 8-10 hours of driving but the same nightly routine.

Don't get me wrong, battery monitors are great to have, especially if you are "Camping out" in the RV. But my use of the truck really doesn't fit that mold.
I would be hard pressed to drain the 4 batteries with a 24 hour trip with the set up I have in the truck.

This is why I am more concerned about while the truck is sitting dormant instead of being used.

Great info on the battery monitors though. Thank you.

 

[Mark_K5LXP]

Just as a data point, wet cell batteries need some kind of activity to keep the electrolyte from stratifying. If it's not kept mixed up periodically by either by motion or equalizing, the uneven concentration of acid will damage the grid, plates and paste. AGM batteries don't have this issue and are a better choice for standby service, where you need a given capacity but infrequently. The downside is AGM costs 2x that flooded does so it's kind of a mixed bag - you might replace AGM half as often but at 2x the cost, it's no cheaper than flooded. But there's a reliability and convenience factor as well, so throwing this out for consideration.

Mark B.
Albuquerque, NM

 

[Dajain]

Just as a data point, wet cell batteries need some kind of activity to keep the electrolyte from stratifying. If it's not kept mixed up periodically by either by motion or equalizing, the uneven concentration of acid will damage the grid, plates and paste. AGM batteries don't have this issue and are a better choice for standby service, where you need a given capacity but infrequently. The downside is AGM costs 2x that flooded does so it's kind of a mixed bag - you might replace AGM half as often but at 2x the cost, it's no cheaper than flooded. But there's a reliability and convenience factor as well, so throwing this out for consideration.

Mark B.
Albuquerque, NM

On another note, lead acid batteries are considered "dead" at 10.5 volts and this is also when damage to the grid starts to happen.

So, which happens first? Damage from under charge or stratifying?

Both are equally bad, but a trickle charge (either battery tender or solar) will prevent the stratify process. It will also prevent the undercharge damage.

 

[Mark_K5LXP]

Damage from under charge or stratifying?

It's an aggregation of time and state of charge. A slightly undercharged battery will take a long time to degrade, a fully discharged battery will degrade much more quickly. A brand new battery kept at full charge but left to stratify will become junk more quickly than one that's used and cycled periodically. So it's not all or nothing but if you have the choice, keeping at full charge is the default, then anything you can do to minimize stratification is a bonus. There are some converters out there (and maybe solar controllers) that do a periodic equalize cycle. That's probably the best of both worlds for batteries that are left idle for extended periods of time. Gel and AGM solve the stratification problem but at a higher acquisition cost, but for some applications it's worth it, such as computer backup battery banks, emergency lighting, etc.

Mark B.
Albuquerque, NM

 

[Dajain]

It's an aggregation of time and state of charge. A slightly undercharged battery will take a long time to degrade, a fully discharged battery will degrade much more quickly. A brand new battery kept at full charge but left to stratify will become junk more quickly than one that's used and cycled periodically. So it's not all or nothing but if you have the choice, keeping at full charge is the default, then anything you can do to minimize stratification is a bonus. There are some converters out there (and maybe solar controllers) that do a periodic equalize cycle. That's probably the best of both worlds for batteries that are left idle for extended periods of time. Gel and AGM solve the stratification problem but at a higher acquisition cost, but for some applications it's worth it, such as computer backup battery banks, emergency lighting, etc.

Mark B.
Albuquerque, NM

And there lies a real issue.
Four lead acid batteries rated for 950 cca cost about $700.
Four AGM batteries rated for 950 cca will cost about $1700.

Hard pill to swallow for something that gets used 5 - 10 nights per year.

A simple answer?
Go out to the truck and start it once a month. The 1000 amp draw of starting the cold 14 liter diesel will stir up any battery. Again, keeping the batteries 100% charged is still the goal so this can happen easily.