Ask anybody a question about RV batteries (same for golf and marine batteries) and you will get either a long response, “Figure out your watts if you want to know your amps, but you don’t have to know your amps, but you should know your amps.” or short responses “Hell, I don’t know.”
Most answers are somewhere in between, and if you ask any follow-up questions at all, you will hear the ultimate fudge-factoring, procrastination-inducing, well-why-did-I-even-bother answer, “It depends.”
Unless you have bladder control issues (and I’m sorry if you do), then “Depends” as an answer sucks.
“How much does this position pay?” It depends. “How do my skills stack up in the workplace?” It depends. “Will you marry me?” It depends. “Should I cut the red or the blue wire?” It depends. I think we can do better than that.
Yes, of course, battery life, charging times all depend on many factors. So does life, but we still seek and find reasonable answers that can guide our decisions and our lifestyle.
We had noticed problems with our lead-acid, factory-installed batteries in our 6-month old RV since the 2nd and 3rd month. We bought it new, but RVs sit on the sales lot for a long time without regular, proper charging and maintenance, so it’s not uncommon for the batteries in a new RV to have lost some life-span by the time you buy it. So we’ve just worked with the factory/warranty to get those replaced as it was becoming a bigger and bigger problem for us.
So what factors go INTO determining your battery’s energy storage, usage and life cycle needs?
HOW OLD ARE THE BATTERIES?
After six months, battery performance starts to deteriorate.
- AGM batteries will start to decline at a rate of 1% each month.
- Normal lead-acid batteries will start to decline at a rate of 2-3% each month (quite a bit faster than AGM batteries).
HOW OLD WERE YOUR BATTERIES WHEN YOU BOUGHT THEM?
Traditional lead-acid deep-cycle batteries will sulfate from sitting more than 3 months without an occasional charge and rarely are new batteries maintained pre-purchase. If you buy new wet acid batteries, be sure they are less than 3 months old. AGM batteries can sit for as long as 1 year before degrading without charge.1) Check the date stamp code on your batteries and make sure you know when they were manufactured.
DO YOU DO REGULAR MAINTENANCE?
Two-thirds of all batteries sold today will need to be replaced within 4 years2)
Maintenance-free is just one of the reasons that newer AGM batteries are so popular. They are sealed so they hold their moisture but have special valves to release occasional nitrogen gas build-ups as “burps” as a Full River battery rep explained it to me. AGM batteries are not without maintenance; however, it’s pretty easy. The basic maintenance is:
- Don’t drain them below 50% which is 12.1 volts.
- Don’t “equalize” AGM batteries unless directed by your manufacturer’s rep.
Your inverter/charger has a setting for the type of batteries you have, usually Gel, Flooded, AGM 1 and AGM 2. AGM 1 allows for equalizing, whereas AGM 2 does not. In most cases, an AGM battery should not need to be equalized because they are sealed, the plates will not lose their electrolytes nor will they be exposed to air (sulfating). Equalizing a battery over-charges them ~29% above their voltage causing heat, bubbling and gassing which you really don’t want (or need) in a sealed AGM battery. (12v * 1.29 = 15.5v) Check your batteries for the exact recommendation and adjust your controller/charger as needed.
For older, common lead-acid batteries they involve more maintenance items:
- Check the fluids regularly in each cell. A 6-volt battery has three (3) 2-volt cells where as a 12-volt battery has six (6) 2-volt cells.
- The fluid is acid so if it gets on your bare hands or clothes, it will burn and “eat” into them.
- The fluid can’t be too low OR too high, only fill to just above the lead plates (about 1/8″ to 1/4″). ONLY fill with distilled water and ONLY when the battery is fully charged.
- If the fluid is too low, below the plates, the plate will sulfate (similar to oxidation). A good battery should not need distilled water added to replace lost electrolytes more than once a year.
- If the batteries are heating up due to over-charging or external temperatures, they will gas so they need to be in a vented compartment away from sparks and people/pets.
- With that gassing comes corrosion to the battery posts, the battery holders/clamps and any other nearby metals.
DO YOU OVERCHARGE THE BATTERIES?
Overcharging the batteries will shorten the life-span and will also lead to over-heating, gassing and possible explosion. As a rule of thumb, you don’t want acid blowing up and flying around in the air. An explosion is not usually fatal but often does involve severe face and eye injuries when working on them.
DO YOU OVER-USE & DRAIN THE BATTERIES?
Undercharging and running down the batteries, while not quite as volatile will permanently damage them and lower their life-cycle rapidly.
Batteries need to be fully charged to 12.6 volts and beyond. A rule of thumb is to over-charge 20% more than the battery’s capacity so a 12-volt battery (12v * 1.2 = 14.4v) should be charged to 14.4 volts. If they aren’t regularly charged beyond 12.6 volts, the cell plates will start to build up. Using a battery creates lead sulfate which builds up – charging the batteries converts that lead sulfate back to charged sulfuric acid. If that build up continues, the batteries peak capacity will drop below 100% (12.6 volts) until it drops so far, that you can’t recover the battery and they stop producing volts/energy. Eighty-six percent (86%) of failed batteries do so because of sulfate and corrosion.3)
Don’t go up and down like a yoyo with your batteries. You may be able to camp for 2-3 days on a single charge – great for you! Once you hit that low point, charge them all the way back up. If you cycle your batteries more often, then make sure each time you charge, you “deep cycle” them, in other words, you took them all the way down to 0-20%, now take them all the way back up at least to 12.6 (100%).
Don’t think just because you charge them more often that you can shortcut the charge level and “top off” the charge at 60 or 80%. You will only reduce the life of your batteries.
If you let your RV set for extended periods of time, shutting off all battery draining items is only one piece of the puzzle. The battery will still drain (called “self-discharging”) and lose energy over time. AGMs lose 1-3% per month and lead-acid lose up to 30% per month when idle. 4). So you need to have a trickle-charger that will cycle them slowly while you’re off doing other, more fun things.
A battery discharged for extended periods of time will form lead hydrate and the battery will short-circuit when charged, permanently damaging the cells. Ten percent (10%) of failed batteries do so because of short-circuits in the cells.5)
WHAT IS THE NORMAL, REGULAR TEMPERATURE EXPOSURE?
Batteries are sensitive to temperature extremes just like we are. A battery and it’s ability to store and produce charge/current is nothing more than a chemical reaction. And that chemical reaction is impacted by extreme temperatures. A modest 77ºF is optimal for a battery. You can think of too much heat as producing a fever but too much cold producing hypothermia. A battery stored/used at 85ºF will have a shortened life-cycle by 28% – on a 4 to 8 year battery, expect to replace them in 3 to 5½ years. A battery stored/used at 95ºF will have a shortened life-cycle by 52% – on a 4 to 8 year battery, expect to replace them in 17 months to 4 years. A battery at freezing temperatures or below will stall the chemical processes needed to store and release energy.
The bottom line is, treat your batteries well and they will treat you with many years of energy. Abuse them if you wish but be prepared for them to abuse your wallet right back or to give up your battery-addicted hobby.
I am working on a new PDF booklet for download that will include RV battery charts. My goal is that I can simply:
- go look at my inverter
- read the current battery voltage
- read the current amp load of everything I’m running at the moment (I have NO interest in micro-managing and calculating everything running in my RV)
- look up those two numbers in a chart and see how long before my battery drops to a level that I don’t want to cross.
Simple enough. I don’t want to calculate amps, volts and watts all the time. I just want to know that I can watch a few shows with the family for 142 minutes if we want.
What kind of shows do we like to watch and how often? It depends.
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