How Much Juice In Your Batteries?
A critical factor for RVers who boondock--camp away from utility hookups--is that of a viable battery bank. Keeping those batteries properly charged can make the difference between an enjoyable experience and a bust. Even more important, a battery that is discharged too much is a battery that will experience a premature death.
How do you know your battery state of charge? Don’t rely on the clever "charge indicators" that most RV manufacturers build into rigs. These "good, weak, charge" meters don’t give you precise enough information. You need an inexpensive digital multimeter. Radio Shack can set you one up for around $20, while Harbor Freight Tools had one on sale today for $2.99--same kind as we use all the time, that’s a WOW!
To properly test an RV "house" battery (the one that powers stuff like inside lights, water pump, furnace motor, etcetera), the battery needs to be at rest. This means not charged within the last hour or so, and with nothing drawing power from it. Since you’ve now read your multimeter instructions, hook the probes up to the battery (best to observe polarity), set the meter from the appropriate voltage range, and check the reading. Now compare to this information:
Volts --- Remaining Capacity
12.63 --- 100%
12.54 --- 90%
12.45 --- 80%
12.36 --- 70%
12.27 --- 60%
12.18 --- 50%
12.09 --- 40%
12.00 --- 30%
11.91 --- 20%
11.82 --- 10%
In our photo, the meter shows 12.30 volts, between 60 & 70 percent of full capacity. The trick is to try and never let your remaining capacity fall below 50%. If you keep it at 50% or more, your batteries will have many more "charge, discharge" cycles before croaking. Print this little chart and tape it on the inside of your battery compartment door.
How do you know your battery state of charge? Don’t rely on the clever "charge indicators" that most RV manufacturers build into rigs. These "good, weak, charge" meters don’t give you precise enough information. You need an inexpensive digital multimeter. Radio Shack can set you one up for around $20, while Harbor Freight Tools had one on sale today for $2.99--same kind as we use all the time, that’s a WOW!
To properly test an RV "house" battery (the one that powers stuff like inside lights, water pump, furnace motor, etcetera), the battery needs to be at rest. This means not charged within the last hour or so, and with nothing drawing power from it. Since you’ve now read your multimeter instructions, hook the probes up to the battery (best to observe polarity), set the meter from the appropriate voltage range, and check the reading. Now compare to this information:
Volts --- Remaining Capacity
12.63 --- 100%
12.54 --- 90%
12.45 --- 80%
12.36 --- 70%
12.27 --- 60%
12.18 --- 50%
12.09 --- 40%
12.00 --- 30%
11.91 --- 20%
11.82 --- 10%
In our photo, the meter shows 12.30 volts, between 60 & 70 percent of full capacity. The trick is to try and never let your remaining capacity fall below 50%. If you keep it at 50% or more, your batteries will have many more "charge, discharge" cycles before croaking. Print this little chart and tape it on the inside of your battery compartment door.
posted by Russ and Tiña De Maris at
4:09 PM
15 Comments:
It looks like 10% should be 11.82 not 12.82. thanks, Michelle
By
Michelle Ress, at 11:06 AM
This post has been removed by a blog administrator.
By
Russ De Maris, at 6:54 PM
this is great for users of 12 volt systems. However, many, if not most, boondockers use 6v systems. what is the chart for those batteries?
By
Anonymous, at 8:00 AM
Would 6 volt batteries be half these amounts?
By
Steve, at 9:24 AM
Great info. Does this also apply to a starting battery in a boat? Does it app;y to a deep cycle battery in a boat? Thanks.
By
Rich, at 9:29 AM
To properly test a batteries "true" state of charge you MUST use a hydrometer. Volt meters can be very misleading and won’t tell you if your battery is getting low on water, which is another great reason to use a hydrometer. E-Z Red S101 - Hydrometer Battery Testers are very inexpensive ($10-$12.00) and work very well for many years if rinsed out after each use. Voltage meters only show open circuit voltage, not specific gravity.
This chart below if followed will show you right away what TRUE state of charge you are at, and if any cell is more than .05 difference then another cell, then you have a cell that may be going bad:
Specific Gravity / Voltage
12V 6V
100% 1.265 12.7 6.3
*75% 1.225 12.4 6.2
50% 1.190 12.2 6.1
25% 1.155 12.0 6.0
Dischg 1.120 11.9 6.0
If your battery does get low on water, use distilled water (not to much or you will delute the state of charge of the battery, and it will need to be recharged before properly testing) bringing the water 1/4" - 1/2" below the ring/well when looking into the cell. If at anytime your batteries water does fall below the plates, that part of the battery is now "no good" no matter what you do! Again, using a voltage meter will never let you see if you are running low on water, all the more reason to pop the caps off and use your hydrometer..
Most R.V.ers, leave their RV plugged into A/C shore power and don't understand their batteries are constantly being charged until unplugged (RV manufacturers tell you thier units cut off the power being supplied once fully charged, NOT!!!. Constantly charging will create heat which will evaporate the water levels, and if the water does go below the plates, that portion of the battery is ruined forever, no matter what you do.. Note: Never add acid to a battery, water is the only part that evaporates!
Also letting a battery just sit is very bad, as a battery will discharge at 1% per day (at 75-80 deg., less in the winter months)and once it falls below 12:40 specific gravity it starts getting sick, called sulfation.
Bottom line: Don't leave your batteries hooked up during the off season!! To get long life always take a fully charged battery (12:65 S.Gravity by using a hydrometer so you know if it is 100%) and then connect it/them to a 1.5 volt battery maintainer. By doing this your battery never falls below 12:40 S.G. (getting sick stage) and will be fully charged when spring comes around, thus giving you much longer life...
Using a hydrometer and maintainer is the only way to go!
By
Anonymous, at 10:28 AM
6 Volt batteries are the only way to go! Two 6 volt batteries give way more power than four 12 volt (group 24)batteries. Testing 6 volt batteries with a hydometer is the same as a 12 volt battery, readings are no differant and specific gravity is the same.
When using a maintainer for two 6 volt batteries in the off season, disconnect the positive cable (This stops the coach from charging the batteries) now you will see there is still a jumper/cable between both batteries making the six volts into a 12 volt system. Take one lead (red)of the maintainer and hook it to the positive side of the first battery, then take the other black end and hook it to the other battery negitive post. You will now be maintaining a 12 volt system.
Two 12 volt batteries hooked together make a 12 volt system, way more powerful than using 12 volt batteries if you have the room. 6 volt batteries have much thicker paste on the plates and can withstand deep dicharges, but you must make sure you never leave your battery/batteries in a discharged state for very long. Doing so will put the battery in a sick state thus cutting off the back half of the life of the battery. Hope this helps guys.
By
Kman, at 10:56 AM
I use the spiral wound Ultima batteries (2) and found them to be very reliable and dependable. But since they are sealed, a multimeter is a great way to check. Alan
By
Anonymous, at 2:17 PM
Checking voltage when the battery is NOT powering a load can give false high readings because the voltmeter draws such a tiny current. To get an accurate battery capacity reading, it's best to test your voltage when the battery is supplying current to a load, such as a fan motor. You can check the voltage anywhere 12v from that battery is supplied. It doesn't have to be at the battery terminals. This is as accurate as a hydrometer as long as you check the water occasionally.
By
Justin, at 2:33 PM
I believe that "kman" mean't in the the start of the 3rd paragraph, 6 volt, instead of 12 volt.
I didn't hear anybody mention deep-cycle 6 volt batteries, or golf-cart batteries, thats what I use.
By
Anonymous, at 2:52 PM
What criteria would you use for AGM batteries?
By
Anonymous, at 5:42 PM
little off the subject but my 99bounder has fried 3 starter battery's when hooked to shore power these battery's are sealed maintenance free (and not cheap) the inverter charges this battery full time and has no cut off, is this standard on all bounders or do i have a problem ?
By
Anonymous, at 6:23 PM
I installed a digital read meter attached to my "D" 12V Lifeline sealed btty which gives me a read 24/7. Lifeline advised to disconnect the negative terminal when storing for a long time. I did and several weeks later the read had fallen from 12.7 to 12.63. Even with the house main switch off, there is still drain, ie: inverter, etc. Additionally I have used 1.5 amp. trickle charges for the past 15 years on all my vehicle btty's. My boat btty is 12 yrs. old and still functioning. My lawn mower btty is 11 years old.
By
Roger, at 6:30 AM
To the owner of the 99 Bounder:
This is typical of some OEM chargers. Look for a 3 stage battery charger such as the Intellipower with Charge Wizzard or others on the market that have a boost charge, desulfation and a maintenance charge. It could also be that your charger has malfunctioned.
By
Anonymous, at 7:51 AM
Note that measuring the static battery voltage only gives a relative estimate of remaining power, as batteries gradually lose the ability to accept a full charge.
By
Anonymous, at 11:42 AM
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