Hello all! I am a first timer and currently fulltiming in my RV. I want to boondock a bit more and feel like my Interstate Batteries HD24-DP may not be up to the task. I was thinking about maybe going with a pair of Trojan T-125s connected in series. What I'm not sure about is, will my converter be able to handle charging these batteries? It's a WFCO WF-8735-P. I guess I'm just wondering if I can swap the battery box on the tongue, throw in the two T-125s, hook them up and BAM I'm done? Thanks in advance for any information! The electrical systems on these things can be a bit complex for the uninitiated...
Thinking about upgrading battery
- Thread starter omguf
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Good choice in batteries. The WFCO will charge them, just may be a little slow to get them topped off. How long are you planning on boondocking How are you planning to charge them while boondocking? Run a generator and charge with your converter? Are you planning on installing solar?
Here's a couple of links on RV electrical, and a lot of information on solar:
http://www.jackdanmayer.com/rv_electrical_and_solar.htm
https://handybobsolar.wordpress.com/
There's another good site that gets recommended on here, but my brain won't bring it up this morning.
Here's a couple of links on RV electrical, and a lot of information on solar:
http://www.jackdanmayer.com/rv_electrical_and_solar.htm
https://handybobsolar.wordpress.com/
There's another good site that gets recommended on here, but my brain won't bring it up this morning.
Gary RV_Wizard
Site Team
Yes you can swap batteries and it will work. The 8735 will charge them, albeit more slowly than a more powerful charger unit would.
The T125 pair will store about 3x the power (amp-hours) of the single Group 24 battery you now have. The good news is that it takes 3x as long to run down, but the bad news is it also takes nearly 3x as long to re-charge. A large (higher amp rate) charger would reduce the time somewhat. A 55A charger would probably cut the time noticeably, but the smaller one still works.
The T125 pair will store about 3x the power (amp-hours) of the single Group 24 battery you now have. The good news is that it takes 3x as long to run down, but the bad news is it also takes nearly 3x as long to re-charge. A large (higher amp rate) charger would reduce the time somewhat. A 55A charger would probably cut the time noticeably, but the smaller one still works.
Hey thanks for the info guys! And sorry for the delay, I've been boondocking!! 
As for recharging, I have a 2000w inverter generator that I use to recharge my current battery. After posting this I realized that the weight on my tongue (where my current battery is installed) would go from 41 lbs (current single 12v) to 132 lbs (twin T125s). I'm not sure if that is going to work. My rig is very light weight and I'm already pretty much at my limit on the tongue (and over all) as it is. I might have to consider a Group 27 battery maybe. That won't give me the AHs the 125s would but anything will be better than the Interstate HDP24 they installed at the lot. I'm usually below 30% in the morning after topping off the evening before and running nothing but my fridge electronics and my furnace blower (I'm even using solar lights inside to keep the draw down). I am looking into installing an ammeter so I can see what's being drawn. I feel like an ammeter should be standard on all RVs/boats... Thanks again for all the info!
As for recharging, I have a 2000w inverter generator that I use to recharge my current battery. After posting this I realized that the weight on my tongue (where my current battery is installed) would go from 41 lbs (current single 12v) to 132 lbs (twin T125s). I'm not sure if that is going to work. My rig is very light weight and I'm already pretty much at my limit on the tongue (and over all) as it is. I might have to consider a Group 27 battery maybe. That won't give me the AHs the 125s would but anything will be better than the Interstate HDP24 they installed at the lot. I'm usually below 30% in the morning after topping off the evening before and running nothing but my fridge electronics and my furnace blower (I'm even using solar lights inside to keep the draw down). I am looking into installing an ammeter so I can see what's being drawn. I feel like an ammeter should be standard on all RVs/boats... Thanks again for all the info!
Gary RV_Wizard
Site Team
Since its the amount of lead plates that is the controlling factor, battery amp-hours are directly proportional to the battery weight.
A Group 27 battery with a 105 AH rating (20 hour rate) would weigh 55 lbs. The higher capacity 115AH in that size weighs 61 lbs.
You can also get a Group 24 size with slightly greater capacity than your present battery, e.g. 85AH weighing in at 47 lbs. The Trojan 24TMX, for example.
A Group 27 battery with a 105 AH rating (20 hour rate) would weigh 55 lbs. The higher capacity 115AH in that size weighs 61 lbs.
You can also get a Group 24 size with slightly greater capacity than your present battery, e.g. 85AH weighing in at 47 lbs. The Trojan 24TMX, for example.
QZ
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Trojan recommends a daily charge of 14.8 volts. Your WFCO will often do 13.6 unless your battery is deeply discharged and often they wont hold for long before going back to 13.6. If you upgrade the converter to something like a Progressive Dynamics PD4655 you will get 14.4 volt charging and it also has a boost button to force it to 14.4. It doesn't sound like much of a difference in voltage but it is. If you do go to Trojans or some other GC2 battery consider upgrading to a boondocker converter that goes to 14.8.
13.6 will charge the battery but it takes a long time. Think of the amps as the diameter of a pipe. Think of the volts as the force pushing on the amps in the pipe. The battery will accept a lot of amps in the early stage of charging and tapers off as the voltage rises. You mentioned amp monitors which can be basic inexpressive models or full function models like Trimetric or Victron. The Trimetric uses a system called RPC return percent of charge. This function counts how many amps were removed from the battery and replaces more than that to account for internal battery resistance and wiring losses.
When mentioning wiring losses no matter what components you use check you terminals at the converter for tightness. It's common for them to loosen. Then check the voltage at those converter terminals while charging then go to your battery and check terminal voltage to determine your voltage drop. Depending on the distance from your converter to the battery it can sometimes be a substantial loss. Many rigs use 6 gauge wire and many times people will upgrade to 4 or even 2. This may seem like a small loss of energy and it is when your rig is sitting on shore power. When you are on genny or solar you want to push everything you can into the battery as fast as you can and shut the geny off.
If you consider solar that's another short book.
13.6 will charge the battery but it takes a long time. Think of the amps as the diameter of a pipe. Think of the volts as the force pushing on the amps in the pipe. The battery will accept a lot of amps in the early stage of charging and tapers off as the voltage rises. You mentioned amp monitors which can be basic inexpressive models or full function models like Trimetric or Victron. The Trimetric uses a system called RPC return percent of charge. This function counts how many amps were removed from the battery and replaces more than that to account for internal battery resistance and wiring losses.
When mentioning wiring losses no matter what components you use check you terminals at the converter for tightness. It's common for them to loosen. Then check the voltage at those converter terminals while charging then go to your battery and check terminal voltage to determine your voltage drop. Depending on the distance from your converter to the battery it can sometimes be a substantial loss. Many rigs use 6 gauge wire and many times people will upgrade to 4 or even 2. This may seem like a small loss of energy and it is when your rig is sitting on shore power. When you are on genny or solar you want to push everything you can into the battery as fast as you can and shut the geny off.
If you consider solar that's another short book.
QZ
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Two gp 24 together should give you 170 AH and weigh 93 pounds. A gp 27 will give about 100 AH and weigh 50 pounds. Two GC2 will give you about 215 AH and weigh 125 pounds. GC2 are taller at about 11 inches compared to the others and are true deep cycle.
Your battery is your bank account balance.
Your discharge is your spending.
Your charging source/ability is your income.
You first want to have enough bank to make it through the night or between the times that you can run the genny or harvest sun.
Your battery is your bank account balance.
Your discharge is your spending.
Your charging source/ability is your income.
You first want to have enough bank to make it through the night or between the times that you can run the genny or harvest sun.
Gary RV_Wizard
Site Team
The WFCO 89xx series is indeed a bit light on charge voltage, with a 13.2v float and 13.6v Absorption charge. Most modern 3-stage chargers float at 13.6v and do absorption and bulk charging at 14.4 of so. But the WFCO will get the job done, albeit a bit slower than some other brands/models.
AStravelers
Well-known member
Be sure to read the RV Electrical System links given earlier and also read these two:
http://www.marxrv.com/12volt/12volt.htm
http://www.marxrv.com/12volt/12volta.htm
There are significant considerations in how far to discharge batteries and just how to charge the battery. Many if not just about all smaller RV's and trailers come with single stage chargers which will take many, many hours to do a decent job of charging your batteries. Just running your generator for an hour or two does not do the job.
Again read the links for much more detailed info.
http://www.marxrv.com/12volt/12volt.htm
http://www.marxrv.com/12volt/12volta.htm
There are significant considerations in how far to discharge batteries and just how to charge the battery. Many if not just about all smaller RV's and trailers come with single stage chargers which will take many, many hours to do a decent job of charging your batteries. Just running your generator for an hour or two does not do the job.
Again read the links for much more detailed info.
Thank you all so much for the info! There's a lot to learn about these systems. I'm still running on the Interstate my TT came with and I'll be boondocking in NC at the end of this month. I want to invest the money in an upgraded system but I want to do it right which is why I greatly appreciate all the info and links you all have sent. So a quick question, I'd like to monitor the charge state of my battery during this upcoming trip. I've wired a voltage gauge into the system that will tell me the current voltage of my battery. Will this be accurate enough to keep an eye on battery level? I noticed a graph in one of the links above that shows voltage vs % battery remaining. I should be able to reference that to determine my % remaining, no? What about when it comes to charge? How can I determine when my battery is fully charged? I'm assuming I can periodically turn off my generator and check my gauge although will that tell me where my battery is at? I thought I had read something about having to let a battery rest with no load for a period of time before you're able to get an accurate reading. Obviously that's out the question since the battery needs to be in near constant operation. What do you guys do to monitor the performance of your battery? I have a voltmeter and a VERY basic understanding of how to use it if that helps.
Gary RV_Wizard
Site Team
There are lithium ion batteries that are designed to be swapped for lead-acid, but to reap all the potential advantages one would need a system designed for them, i.e. containing a LI monitoring/management device. I think some packaged 12v LI batteries have an individual monitor built into each battery.
Back2PA
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And re lithium there are other issues I?ve read about, such as ambient temperature, which could be a real issue with a tongue-mounted battery
AStravelers
Well-known member
You can make an estimate of the SOC (State of Charge) by using the voltage readings.omguf said:
-- If you have been charging the battery it needs to rest for an hour or two, with a minor load on it. You probably have a phantom (background load of the fridge control board and other stuff) of 1.5 to 2 amps. For a minor load, just turn on one light fixture with one bulb. Assuming the bulb is not LED, the incandescent or florescent light will draw about 3 amps. Leave that load on the battery check the battery voltage every 15 minutes until the voltage stabilizes. No need to turn the light off, just be sure that is the only thing on.
-- If you not been charging your battery, just turn all the lights off, no inverter, TV, laptop charging, etc and read the voltage.
It is much easier and more accurate to have a battery monitor to "know" just how many amp hours (AH) have been used or put back in while charging.
Kevin Means
Site Team
Omguff, if you plan on doing a fair amount of boondocking, I assure you that you'll be much happier with a good battery monitor than with a volt meter. As Al inferred, a battery's voltage is actually a pretty inaccurate way of determining its State Of Charge, unless you disconnect the battery from all loads for at least an hour. Who wants to do that when you're camping?
Battery monitors are programmable for the amp hour (AH) capacity of your battery bank, and they can display how many amps are going in, or out, of your batteries at any given time. Because of that, battery monitors can display your battery bank's true SOC, even when under a load or when charging.
Our Trimetric RV 2030 can also display (in percentage) how much battery capacity we have remaining, which is a VERY useful feature when boondocking. A battery's voltage indication can't give you that information. I like to say that boondocking without a good battery monitor is like driving without a fuel gauge.
Kev
Battery monitors are programmable for the amp hour (AH) capacity of your battery bank, and they can display how many amps are going in, or out, of your batteries at any given time. Because of that, battery monitors can display your battery bank's true SOC, even when under a load or when charging.
Our Trimetric RV 2030 can also display (in percentage) how much battery capacity we have remaining, which is a VERY useful feature when boondocking. A battery's voltage indication can't give you that information. I like to say that boondocking without a good battery monitor is like driving without a fuel gauge.
Kev
Gary RV_Wizard
Site Team
For the basics on battery types for RV usage, try my article on http://www.rvforum.net/miscfiles/Choosing_right_battery.pdf
Mostly, though, you need to think about your power consumption (amp-hours used per day) and then get enough battery capacity (larger sizes or or more of them) to handle that power between chargings. If you don't plan for your power consumption, everything else is just guesswork. And a battery monitor won't help - dead is still dead.
Mostly, though, you need to think about your power consumption (amp-hours used per day) and then get enough battery capacity (larger sizes or or more of them) to handle that power between chargings. If you don't plan for your power consumption, everything else is just guesswork. And a battery monitor won't help - dead is still dead.
