I have a large (group 31) AGM deep cycle battery I use as my house battery. It is about 2 years old and has had what I would call moderate use. So far it has the winch, fridge, water pump, and charging ports hooked up to it. Drove about 7 hours last week to destination. Shut everything down except fridge. Battery was only indicating a charge of around 12 volts. Fridge ran fine until battery hits about 10.5 volts, at which point the fridge is designed to cut out, which it did. Fridge only took about 24 hours to reach shut off this last trip, whereas before it would run for days. I put a trickle charger on the battery last night and it charged overnight to 14.4 volts. I would have thought the alternator would have done the same thing on a 7 hour drive. Any theories or advice are welcome, as I am not that experienced with deep cycles or battery charging physics. Is my alternator defective? Battery aging means it won't accept charges of certain characteristics? My starting battery is AGM but not deep cycle, and is charging off the identical alternator. I checked both batteries with the multimeter last night at the same time.
AGM battery charging/discharging (2 Viewers)
- Thread starter jgranthevagrant
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An older worn out battery won't take/keep a charge and may or may not even reach the usual 14.4V that most chargers should provide. I would think that if it is good, it should be about 12.6V with no load for sure after 7hrs on the alternator. But with the fridge on, it could well be on the mid to low 12V side with the engine off, depending on the fridge load. Although it should rebound quickly when the fridge goes off. Your battery is only 2 years old, it should be OK if it has not been misused. But if you did let it run down to 10.5V many times before that is quite a heavy use from my perspective. I would test it. It's pretty easy to figure out by trial and error, if you have a good charger to try things with. Charge it, check the voltage as you do and when you're done charging, and then put a load on it and see what happens voltagewise etc. You could do something as simple as putting a light bulb on it and timing it to get a feel for the capacity if you don't have meters. Or just use the fridge as a load after charging it fully with the charger and check again again how long it runs after full charge. Try various things and you should be able to tell if it's in decent shape. Note that it's not a given that the battery is good or even fully charged for that matter if it shows 14.4 with the charger/alternator on, the current matters as an indicator. And the kind of charger (smart or not etc) matters also, of course.
As to your alternator it is unlikely it would be bad if your main starting battery appears to be charged correctly (what was that voltage with engine on and off?). Again, fairly easy to get a feel for, see if it provides around 14.4V on the batteries when first charging them after a start. If it does, it's probably OK I would think. The alternator should be capable of enough current to bring even a low battery to 14V in a short time.
Is it possible that the fridge ran for a shorter time because the temp was higher than usual? That can make a big difference.
How are the 2 batteries connected?
What truck? What alternator?
As to your alternator it is unlikely it would be bad if your main starting battery appears to be charged correctly (what was that voltage with engine on and off?). Again, fairly easy to get a feel for, see if it provides around 14.4V on the batteries when first charging them after a start. If it does, it's probably OK I would think. The alternator should be capable of enough current to bring even a low battery to 14V in a short time.
Is it possible that the fridge ran for a shorter time because the temp was higher than usual? That can make a big difference.
How are the 2 batteries connected?
What truck? What alternator?
I’ve had 3 agms of different brands as house 2nd batteries. They all started to lose AH capacity around 18 months to 2 years similar to your problems. I would suggest a DC to DC charger, smart charger via 110v or solar, or just go lithium. Our alternators put out 13.9 volts and have trouble handling charging an agm to 100%. If that house battery has only seen alternator charging, it likely never got to a 100% charge except when new. AGMs hate to be below 100% as they degrade and desulfate losing their capacity. Heat also plays an issue in my opinion with AGMs. They seem to be a great battery for trailers, RVs and boats since they aren’t stored in an engine and typically are hooked up to “shore power” when not in use. 4x4 trucks with the battery in the engine bay is a different animal due to heat and lack of “shore charging”.
Ditto hooking up AGM batteries especially via a multi-stage quality charger (or solar with AGM profile ala the controller). I've been getting 10-years out of my Odyssey batteries (starting and aux locations)...by keeping them on a charger when the rig is sitting not being used.
- Thread starter
- #6
Thanks for the input. I tested with the fridge after I charged it yesterday. It went about 6 hours. I will drag it out and take it into the place I got it for testing. Just trying to avoid the hassle of that. I talked to some people and researched a bit on lithiums. Conclusion was they were not good for winching? I used my winch once this winter to respool the rope. Could have finished off the battery? I should also note that the house battery and start battery are never linked. I can't afford a dead start battery when it is -25. The house battery is charged off its own alternator. Looks like if I get another AGM I will be monitoring and maintaining more closely.
you have 2 alternators?
So now your fridge only went 6 hrs instead of 24hrs as just before? That is a big change. But how do you know for sure the battery was fully charged? If it was really discharged (10.5V etc) a trickle charger may not have brought it back to full charge in a day.
So now your fridge only went 6 hrs instead of 24hrs as just before? That is a big change. But how do you know for sure the battery was fully charged? If it was really discharged (10.5V etc) a trickle charger may not have brought it back to full charge in a day.
- Thread starter
- #9
Yes I run the second alternator where an AC compressor would be in a U.S or California truck. True, I don't know for sure if the battery was charged beyond trusting the multimeter and the charger saying "charged". Yes, the second alternator is somewhat unusual. Very important to keep the starting battery strong if starting way below zero, which I do sometimes. I read about a lot of people having problems with linked batteries as well. Identical size and age of batteries, that kind of thing.
well, it seems to me that only one, let alone two, alternators should easily be able to keep up with a fridge. Not understanding why you felt the need to have a second one, TBH. The fridge may use 5A a third or half of the time, an alternator should typically be able to produce about 100A whenever the engine is running. No contest. So, your system should work in principle.
Then either you misinterpreted what you saw (unlikely of course), some unusual circumstance made things weird, or the battery and/or alternator are not doing what they should. Those can be fairly easily tested for as mentioned earlier, either with dedicated tools or some DIY approach. I would think it best to approach things systematically. I have played a lot with old and bad deep discharge lead acid batteries trying to find some good ones among a bunch of unknown ones, and after a bunch of tests had to pretty much conclude that the only real way to figure out how good the battery is is with a full discharge test with an appropriate load. Trusting the voltages just isn't foolproof, there can be weird stuff happening. I've had batteries that could be raised to 14V in no time at all, could stay at 12.6 all day long and had no capacity at all. I've had batteries where I could not get the voltage to go above 12V no matter what I tried, etc...
But maybe it's not complicated after all, maybe the battery is just bad or worn out. 2 years is not ridiculously short actually. I remember buying dual purpose starting / deep discharge batteries and they had only one year (IIRC) warranty, I assume because they typically don't last as long as starting batteries.
Anyway, I'm sure you will figure it out shortly.
Then either you misinterpreted what you saw (unlikely of course), some unusual circumstance made things weird, or the battery and/or alternator are not doing what they should. Those can be fairly easily tested for as mentioned earlier, either with dedicated tools or some DIY approach. I would think it best to approach things systematically. I have played a lot with old and bad deep discharge lead acid batteries trying to find some good ones among a bunch of unknown ones, and after a bunch of tests had to pretty much conclude that the only real way to figure out how good the battery is is with a full discharge test with an appropriate load. Trusting the voltages just isn't foolproof, there can be weird stuff happening. I've had batteries that could be raised to 14V in no time at all, could stay at 12.6 all day long and had no capacity at all. I've had batteries where I could not get the voltage to go above 12V no matter what I tried, etc...
But maybe it's not complicated after all, maybe the battery is just bad or worn out. 2 years is not ridiculously short actually. I remember buying dual purpose starting / deep discharge batteries and they had only one year (IIRC) warranty, I assume because they typically don't last as long as starting batteries.
Anyway, I'm sure you will figure it out shortly.
- Thread starter
- #11
I have the original stock alternators for the 22re motor which produce about 60 amps. Should still be able to more than keep up to the fridge, which is the only thing running steadily. I will take the battery in for a test and go from there.
- Thread starter
- #12
Update: took battery in for testing. Predictably enough, it failed, so they gave me a new one under warranty. Not really sure what I did that was so damaging in under 2 years. Winching? Looks like I will be sharper about keeping it charged at least at home. Any particular home (110v) type of charger that is better than others for charging deep cycle AGMs? I will look further at solar for maintaining the battery while truck is parked for a week. It's just not in the budget right at the moment.
FWIW, I did have trouble with Exide Orbital AGM batteries which exhibited similar/same as you described back in '05 and '06...got a refund and went to Odysseys and never looked back. No other changes were made to my electrical system: Just the swapped from Exide Orbital to Odysseys. 
^^ Not too surprising. Good they gave you one. TBH, I was surprised when I read you mentioning the (potential?) winch use. Very high currents like winching seem to fall more under the starting battery strong points than the deep discharge ones. But I have not looked into that TBF.
I think that some AGMs do need a higher voltage for charging than regular FLAs. So, if that is yours, you may want to make sure that the charger can accommodate that.
I think that some AGMs do need a higher voltage for charging than regular FLAs. So, if that is yours, you may want to make sure that the charger can accommodate that.
- Thread starter
- #15
The only thing I checked regarding winch use was with Battle Born batteries. Pretty sure they said to avoid winching with lithium batteries, so I stuck with AGM. I will look around for another charger. My charger seems pretty basic. Does 6 and 12 volts, with 3 settings. Brand is Schumacher, like the F1 driver. Fairly sure it is not a "smart" charger.
I've had great performance from my aux (house) AGM charged by my stock alternator through a Sure Power isolator that was a replacement for a lead acid deep cycle back in 2013. It's a Die Hard Platinum 135 RC, group 34 (actually a rebranded Odyssey by Sears). This batt runs a winch, Puma air compressor, fridge, 2000 watt inverter, 12v outlet (for misc use) and a 12v charge line to my squaredrop trailer's batt to charge on the road. My rule with the winch is: the engine must be running to operate. I think it may hurt your AGM to run the winch without your engine running. I've got a 125 watt portable solar panel to recharge it in camp. In the direct sunlight, my fridge can't tell the difference between solar charging or engine running. The batt in my trailer is also an AGM deep cycle, but currently it's duties are much simpler. It runs a water pump, cabin lights and maybe charging a USB device or 2.
- Thread starter
- #17
I intend to be much more careful with this one. I did winch with the engine off, just to respool the rope. Probably didn't help. Time to get after the solar. Not sure where I'm going to put that.
In direct sun
But seriously, if I were to add solar for my starting battery I would probably just get a portable panel with kickstand and built in controller and just jumper to the battery when in camp.
As far as properly charging AGM, the factory charging system is not designed to do this and you will never get a full charge as mentioned previously leading to sulfation and premature failure. Why AGM? What do you have against FLA?
What vehicle do you have?
I can't answer for @jgranthevagrant , but for me, at the time (2013) when my aux batt needed replacing, AGM was supposed to be superior. It's worked well for me and my solar controller has AGM charging mode, so for as long as it lasts, it's what I use. I've read that for perfomance and longevity, lithium is the new leader. But the temps that lithium batts are used and charged without damage concern me. In another thread, it was mentioned that:
"Having a BMS is CRITICAL with lithium batteries as they cannot be charged below 32°F and above 122°F, safe discharge also has to be within 14°F - 167°F. Working outside of these parameters will damage the battery permanently."
For most folks that live in the U.S. sun belt, it's not a big concern. But where I live, the winter creates some challenges that I don't feel, at this point, that it's worth the hassle to mod my rig just to run a lithium battery. YMMV of course.
"Having a BMS is CRITICAL with lithium batteries as they cannot be charged below 32°F and above 122°F, safe discharge also has to be within 14°F - 167°F. Working outside of these parameters will damage the battery permanently."
For most folks that live in the U.S. sun belt, it's not a big concern. But where I live, the winter creates some challenges that I don't feel, at this point, that it's worth the hassle to mod my rig just to run a lithium battery. YMMV of course.
LiFePo4 drop in batteries continue to evolve and innovate and drop in price. Battleborn has their 100ah made in Nevada battery at only $799 now with a 10-yr warranty. They do a heated battery for $100 more. Relion does a Low Temp battery also with internal heated built in. 12V 100Ah Deep Cycle Cold Weather Lithium Batteries | RELiON - https://relionbattery.com/products/lithium/rb100-lt
There are a few more low temp or heated options for people in colder climates. Heat is the enemy to all batteries including LiFePo4. With that said I have done dual battery installs in the engine bay with LiFePo4 with no reported problems. I know @Hyup and @Road Apple both have theirs in the 80 engine bay. The efficiency of power is unreal vs lead batteries. It’s slowly becoming a no brainer for people who need 12v parked power. I have ran appliances up to 70-100 amps for the xtended periods but winching is gonna be too much for any drop in sold in the USA. My winch is hooked to my starting battery for that reason.
There are a few more low temp or heated options for people in colder climates. Heat is the enemy to all batteries including LiFePo4. With that said I have done dual battery installs in the engine bay with LiFePo4 with no reported problems. I know @Hyup and @Road Apple both have theirs in the 80 engine bay. The efficiency of power is unreal vs lead batteries. It’s slowly becoming a no brainer for people who need 12v parked power. I have ran appliances up to 70-100 amps for the xtended periods but winching is gonna be too much for any drop in sold in the USA. My winch is hooked to my starting battery for that reason.
