Post by cowcharge on May 11, 2015 9:56:14 GMT -8
Hey all! I just finished writing an answer to someone who asked for some battery info, and thought that my thoughts on AGMs might help someone decide what kind of battery to buy (and save them some serious money). I know this stuff has come up in other threads, but I thought it deserved its own thread, so here goes!
First though, a disclaimer. My thoughts are based on my goal of building a 22.5' camper, capable of running pretty much any damn electrical thing I want, while minimizing (if not eliminating) generator or hookup use. I know most of you guys have smaller trailers, and are more interested in the vintage aspects and "simple" camping than being able to full-time with a modern, electricity-based lifestyle. If I had a Compact with its space and weight limitations, and was just running a few lights and a radio, then I might well go for a single, smaller 12v battery instead of the big ones I've got, but it would almost certainly still be a "wet" battery. And I'm pretty sure I would still want to run more stuff than the rest of you because I can only read for so long, lol.
So, back to business. AGMs? Nah, not for me, thanks (even if I could afford one). The only advantages they have are that you can place them in weird spaces at any angle and they aren't supposed to leak, they handle extreme vibration better, you don't have to vent them or put them in special boxes (although you should, for safety's sake), and that you don't have to add water. Which really just means that you can't add water, which is a disadvantage IMO, because if they do get seriously overcharged there's nothing you can do but replace them, for another $600. That's what I paid for my whole camper!
I check the water in my batteries every time I go out, and so far I've only had to add water twice in a year and a half of being constantly hooked up to a 210-watt solar panel, and they weren't even that low, the plates were all still covered (which is the critical thing to watch for). I just keep a gallon of distilled water in the camper, and the only reason I'm not still on the first gallon is that it froze and cracked the jug because I hadn't used enough of it yet! Wet battery maintenance is easy, and since I'm into the whole challenge of electrical efficiency/solar stuff and again, running any damn electrical thing I want, I enjoy it. And every time I go out to the camper, assuming the solar panel hasn't been covered with snow or leaves for the last month, my solar charge controller is happily blinking away on float (maintenance) charge, with full batteries ready to go.
Even a converter hooked up to full-time shore power has a hard time reaching full charge when the battery's in use, because the voltages are too low, for wet batteries anyway. I haven't researched any specific manufacture-recommended charging voltages for any particular AGMs to see if any of them match converter voltages because I'm not using them, but they are all lower than wet batteries. And it's much more critical that you charge them at the right voltages, both for safety and for longevity, than it is for wet batteries. If you overcharge a wet battery, within reason you can just add water and everything's fine again. And just a glance inside the caps will tell you if that's going on, while an AGM just sits there with a blank look on its face until you notice it failing, and by then it's too late. And the charging amps on converters taper off way too soon no matter what kind of battery it is. It might reach full charge about a month after you get home, but converter inadequacies are a whole other discussion...
The disadvantages of AGMs are:
1. Price: $600+ for a Trojan 230ah 12v AGM, my two 6v Duracell golf cart batteries of the same capacity (well-made by Deka) were $230 for the pair (at Sam's Club, East coast, I understand they're labelled under different brands out West).
2. Weight: AGMs weigh more per amp-hour than wet batteries. That single Trojan AGM mentioned above weighs about 30 pounds more (158 pounds) than my two "wets", for the same capacity. Do you really want to move one of those around at your age?
3. Slow charging speed/"AGMs don't gas"/"they're maintenance free": ALL lead-acid batteries gas during charging, because the same chemical reaction occurs in every lead-acid battery, wet or sealed. If you add electricity to acid, you produce gas, period. The reason salesmen can say that "AGMs don't gas" with a somewhat clear conscience is that they're sealed up to a certain vapor pressure, that isn't supposed to be exceeded during normal charging. So if everything goes according to plan, they won't let gas out of the battery case. Sealing them like that though, means you have to charge them at a lower voltage so that they don't produce as much gas as a vented wet battery and blow the safety valves. Which means longer generator runs to charge an AGM, or if you use solar charging, more chance of running out of sun before you're fully charged. If they didn't gas, they wouldn't need safety valves.
4. No access to the electrolyte. The ONLY way to accurately get the true state of charge in a battery is to dip a hydrometer in the acid and check the specific gravity, which you obviously can't do with a sealed battery. A multimeter voltage reading is helpful, but not as accurate as a hydrometer. And those electronic battery managers use assumptions and voltage readings to calculate the state of charge, which is not as accurate, and can often be way off, making it so that your batteries never get a full charge, even though every LED is green. Ever. Ever see a big camper loaded with solar panels but they're still running a generator all evening to run their TV? Or an RV dealer's solar-loaded demo trailer that's still always hooked up to shore power? Those are tell-tale signs of someone who either didn't know how to build a solar system properly (virtually ALL RV dealers, they probably used way too small wires), or someone who doesn't know how to, or can't because of equipment inadequacies, monitor and maintain their solar system properly. And most of them have no idea why their thousands of dollars' worth of solar equipment can't keep their batteries charged, so they just buy more solar panels (which the cynical part of me thinks is the reason the dealers use too-small wires in the first place. But I'm not sure which is worse, regular old dishonesty, or ignorance in their chosen profession.
5. Higher susceptibility to improper charging voltages. Since most chargers and converters have set voltages that you can't change, if you don't pick one that has the exact voltages your AGM manufacturer advises, you will either charge even slower if the voltages are low, or you will overcharge to some degree if they are higher. If they're high enough, the AGM will gas to the point where the safety valves blow, and you'll lose some gas at the very least, which means some lost capacity because you can't replace the lost electrolyte in a sealed battery. And on top of that, now you have a gassing, probably neglected battery, in a probably unvented battery compartment, probably right under your butt under the dinette seat (because who needs venting with batteries that "don't gas", right?). If the over-voltage is high and fast enough, or the battery has faulty safety valves, you can even blow an AGM apart like the pic in Vik's thread. Not easily, but it can be done with an extreme charger mismatch or malfunction. While if you seriously overcharge a wet battery (and pretty much totally neglect its maintenance), it will gas excessively too, and if not checked in time, could "boil" your batteries dry, or even explode/start a fire. But if they are properly installed and vented and maintained and monitored, it's much harder to reach that point than it is with an AGM, just because of the higher normal voltages the batteries are built to handle, the fact that wet batteries can vent all the time and so don't build up pressure, and the fact that AGM salesmen have everyone convinced that they are fool-proof, so they feel they can ignore their batteries, not vent their boxes, etc.
The only way I might be in favor of an AGM in a camper is if it were being used for heavy off-road stuff. Real heavy.
And by the way, there is no such thing as a lead-acid battery that can be drained flat without damage. No way, no how. Not until someone invents a way to make the chemical reaction perfectly efficient (good luck).
(clap clap)
And that's all the television there is!
First though, a disclaimer. My thoughts are based on my goal of building a 22.5' camper, capable of running pretty much any damn electrical thing I want, while minimizing (if not eliminating) generator or hookup use. I know most of you guys have smaller trailers, and are more interested in the vintage aspects and "simple" camping than being able to full-time with a modern, electricity-based lifestyle. If I had a Compact with its space and weight limitations, and was just running a few lights and a radio, then I might well go for a single, smaller 12v battery instead of the big ones I've got, but it would almost certainly still be a "wet" battery. And I'm pretty sure I would still want to run more stuff than the rest of you because I can only read for so long, lol.
So, back to business. AGMs? Nah, not for me, thanks (even if I could afford one). The only advantages they have are that you can place them in weird spaces at any angle and they aren't supposed to leak, they handle extreme vibration better, you don't have to vent them or put them in special boxes (although you should, for safety's sake), and that you don't have to add water. Which really just means that you can't add water, which is a disadvantage IMO, because if they do get seriously overcharged there's nothing you can do but replace them, for another $600. That's what I paid for my whole camper!
I check the water in my batteries every time I go out, and so far I've only had to add water twice in a year and a half of being constantly hooked up to a 210-watt solar panel, and they weren't even that low, the plates were all still covered (which is the critical thing to watch for). I just keep a gallon of distilled water in the camper, and the only reason I'm not still on the first gallon is that it froze and cracked the jug because I hadn't used enough of it yet! Wet battery maintenance is easy, and since I'm into the whole challenge of electrical efficiency/solar stuff and again, running any damn electrical thing I want, I enjoy it. And every time I go out to the camper, assuming the solar panel hasn't been covered with snow or leaves for the last month, my solar charge controller is happily blinking away on float (maintenance) charge, with full batteries ready to go.
Even a converter hooked up to full-time shore power has a hard time reaching full charge when the battery's in use, because the voltages are too low, for wet batteries anyway. I haven't researched any specific manufacture-recommended charging voltages for any particular AGMs to see if any of them match converter voltages because I'm not using them, but they are all lower than wet batteries. And it's much more critical that you charge them at the right voltages, both for safety and for longevity, than it is for wet batteries. If you overcharge a wet battery, within reason you can just add water and everything's fine again. And just a glance inside the caps will tell you if that's going on, while an AGM just sits there with a blank look on its face until you notice it failing, and by then it's too late. And the charging amps on converters taper off way too soon no matter what kind of battery it is. It might reach full charge about a month after you get home, but converter inadequacies are a whole other discussion...
The disadvantages of AGMs are:
1. Price: $600+ for a Trojan 230ah 12v AGM, my two 6v Duracell golf cart batteries of the same capacity (well-made by Deka) were $230 for the pair (at Sam's Club, East coast, I understand they're labelled under different brands out West).
2. Weight: AGMs weigh more per amp-hour than wet batteries. That single Trojan AGM mentioned above weighs about 30 pounds more (158 pounds) than my two "wets", for the same capacity. Do you really want to move one of those around at your age?
3. Slow charging speed/"AGMs don't gas"/"they're maintenance free": ALL lead-acid batteries gas during charging, because the same chemical reaction occurs in every lead-acid battery, wet or sealed. If you add electricity to acid, you produce gas, period. The reason salesmen can say that "AGMs don't gas" with a somewhat clear conscience is that they're sealed up to a certain vapor pressure, that isn't supposed to be exceeded during normal charging. So if everything goes according to plan, they won't let gas out of the battery case. Sealing them like that though, means you have to charge them at a lower voltage so that they don't produce as much gas as a vented wet battery and blow the safety valves. Which means longer generator runs to charge an AGM, or if you use solar charging, more chance of running out of sun before you're fully charged. If they didn't gas, they wouldn't need safety valves.
4. No access to the electrolyte. The ONLY way to accurately get the true state of charge in a battery is to dip a hydrometer in the acid and check the specific gravity, which you obviously can't do with a sealed battery. A multimeter voltage reading is helpful, but not as accurate as a hydrometer. And those electronic battery managers use assumptions and voltage readings to calculate the state of charge, which is not as accurate, and can often be way off, making it so that your batteries never get a full charge, even though every LED is green. Ever. Ever see a big camper loaded with solar panels but they're still running a generator all evening to run their TV? Or an RV dealer's solar-loaded demo trailer that's still always hooked up to shore power? Those are tell-tale signs of someone who either didn't know how to build a solar system properly (virtually ALL RV dealers, they probably used way too small wires), or someone who doesn't know how to, or can't because of equipment inadequacies, monitor and maintain their solar system properly. And most of them have no idea why their thousands of dollars' worth of solar equipment can't keep their batteries charged, so they just buy more solar panels (which the cynical part of me thinks is the reason the dealers use too-small wires in the first place. But I'm not sure which is worse, regular old dishonesty, or ignorance in their chosen profession.
5. Higher susceptibility to improper charging voltages. Since most chargers and converters have set voltages that you can't change, if you don't pick one that has the exact voltages your AGM manufacturer advises, you will either charge even slower if the voltages are low, or you will overcharge to some degree if they are higher. If they're high enough, the AGM will gas to the point where the safety valves blow, and you'll lose some gas at the very least, which means some lost capacity because you can't replace the lost electrolyte in a sealed battery. And on top of that, now you have a gassing, probably neglected battery, in a probably unvented battery compartment, probably right under your butt under the dinette seat (because who needs venting with batteries that "don't gas", right?). If the over-voltage is high and fast enough, or the battery has faulty safety valves, you can even blow an AGM apart like the pic in Vik's thread. Not easily, but it can be done with an extreme charger mismatch or malfunction. While if you seriously overcharge a wet battery (and pretty much totally neglect its maintenance), it will gas excessively too, and if not checked in time, could "boil" your batteries dry, or even explode/start a fire. But if they are properly installed and vented and maintained and monitored, it's much harder to reach that point than it is with an AGM, just because of the higher normal voltages the batteries are built to handle, the fact that wet batteries can vent all the time and so don't build up pressure, and the fact that AGM salesmen have everyone convinced that they are fool-proof, so they feel they can ignore their batteries, not vent their boxes, etc.
The only way I might be in favor of an AGM in a camper is if it were being used for heavy off-road stuff. Real heavy.
And by the way, there is no such thing as a lead-acid battery that can be drained flat without damage. No way, no how. Not until someone invents a way to make the chemical reaction perfectly efficient (good luck).
(clap clap)
And that's all the television there is!
