Batteries

I’m really unknowing in all this so bare with me if my question seems dumb, as it probably is. Why is it so important to never let my batteries go below 12.1?

Full charge on a 12 volt battery is about 12.6 volts.  12.1 volts is about 50% charge.  A standard lead acid battery should never be allowed to go below 50% charge.  Each time doing that hurts its ability to fully recharge.  Do it too often and the battery will fail to hold a complete charge.  So the rule of thumb for those with in coach volt meters is to watch the voltage and recharge if getting close to 12.1 volts.  If you have a energy management system like the Bogart Trimetric 2030 you can watch that instead for a much more accurate reading.  But watching the voltage and staying above 12.1 will help.

I’m really unknowing in all this so bare with me if my question seems dumb, as it probably is. Why is it so important to never let my batteries go below 12.1?

The simple answer is because everyone says so.  

You do ask a very good question.  I am no expert, but from what I gather, the battery gets damaged when you get below 12.1 volts.  If you drained it one time down to 11.9V, I doubt you would do significant permanent harm, but doing so repeatedly is something else.  With each incident, a full charge is less full than the time prior.

I have learned to be anal about that 12.1V number.  Draining to no less than 12.1V is working well for us.  But I don't wait until it gets to 12.1V.  Most often I charge at a higher voltage to avoid excessive generator run times.  If we plan to spend an evening inside, staying up late watching a movie and such, I will plan ahead and charge the batteries using a strong external 40 amp step charger with the generator, anticipating an extended drain in the evening.  FYI: Our on-board Tripp-Lite inverter/charger has a max of 20 amps hence using the 40 amp external charger to reduce generator run times.

Oh, I see jatrax commented just above me.  I like his reply.

Thanks, I see where the 12.1 makes sense as basic guide. I only have 12 volt batteries in my unit and I install new batteries every year. I don’t dry camp a lot so I guess I wouldn’t need to worry too much about going under 12.1 now and then.

Just curious but why do you install new batteries every year?  They should last 5 to 6 years with a little care.  Are they going bad?  If so something is wrong with your charging system.

They are never 100% after a year and they come with a one year warranty. So they offer new replacements.  Why wouldn’t I change them out; it only costs me the time I spend changing them out.

They are never 100% after a year and they come with a one year warranty. So they offer new replacements.  Why wouldn’t I change them out; it only costs me the time I spend changing them out.

Who is the vendor? I am guessing a big box store, as a smaller vendor could not afford that.

Our battery supplier also has a warranty, but the first thing that is done with warranty returns when they hit his shop is they get charged and tested, If they are OK, the shop returns them to you and tells you the problem is in your charging. We used Interstate battery before our present vendor, and their policy was the same.

Even with Autozone/O'Reileys/Advance Discount if you return a battery for warranty, the replacement is only covered for the duration of the original purchase .

Example - My co-worker has a 2005 Chevy Colorado that has regularly gone through a battery every 2.5 years since new. He buys a 3-yr replacement warranty battery, and they replace it once. I started working with him in 2010, and he had just gotten a free new replacement of the first battery he bought. (To replace the factory battery) In mid 2012, that one failed and they denied a free replacement.
He bought another, it lasted into 2015 when he got another free replacement. This last fall THAT one failed, and he was denied again for a freebee. The new one he bought should be the last, as he is expecting to replace the truck soon.


So... I guess enjoy the free battery train while it lasts.

About the volt meter I installed in our PC.  It measures the voltage where I wired it into the stove hood monitor panel.  It is NOT measuring across the battery terminals.  When I turn on a light or two, the voltage doesn't change.  But if we turn on more things, the voltage drops a little.  When I turn off everything again, the voltage increases again.  So during a heavy-use evening the voltage can drop significantly.  Because I maintain the batteries well, it does not drop below 12.1V.  If memory serves me well, the drop is as much as 0.3 volts pending what we have running.

I should perform this experiment.
- Using a hand-held volt meter, measure the voltage across the two 6V batteries with everything off.
- Then turn on a bunch of stuff to get the voltage dropping significantly on the volt meter I installed.
- Then measure the voltage across the two 6V batteries again.
It would tell me if it is better to wire the volt meter across the batteries to avoid the fluctuating read-out.

To you with a serious battery monitor, do you see the same fluctuations I do with our simple volt meter?

Ron, a voltage drop when using any significant amount of battery power is normal.

The 'proper' test of battery voltage is:
- disconnect battery from any load
- charge battery fully
- wait at least 1 hour after charge complete
- test voltage

That will give you the only 'true' voltage.  You cannot get a true voltage when the battery is under load.  But that is really only for testing a suspect battery.  A volt meter in line as you have gives you an instant reading on the state of the battery relative to normal operations.  Which is all you need to tell how things are going.

But any load on the battery will pull the voltage down as long as it is present.  That is just how the lead - acid cycle works.

Other batteries, particularly Lithium have different load curves and their voltage will react differently to a load.

They are never 100% after a year and they come with a one year warranty. So they offer new replacements.  Why wouldn’t I change them out; it only costs me the time I spend changing them out.

Well, if you get a free one every year then I guess there isn't any reason to not change them out.

I was just concerned that something was wrong with your charger since under normal use you should get 3 to 5 years and with care perhaps 7 years on a battery.  Are you installing deep cycle batteries or just off the shelf 12 volt ones?

Ron, a voltage drop when using any significant amount of battery power is normal.

The 'proper' test of battery voltage is:
- disconnect battery from any load
- charge battery fully
- wait at least 1 hour after charge complete
- test voltage

That will give you the only 'true' voltage.  You cannot get a true voltage when the battery is under load.  But that is really only for testing a suspect battery.  A volt meter in line as you have gives you an instant reading on the state of the battery relative to normal operations.  Which is all you need to tell how things are going.

But any load on the battery will pull the voltage down as long as it is present.  That is just how the lead - acid cycle works.

Other batteries, particularly Lithium have different load curves and their voltage will react differently to a load.

Thank you for the explanation jatrax!

Sorry it took me so long to reply, I don’t get on here every day. Being retired I’m so busy I wonder how I ever had time to have a job. 

I buy my batteries at Costco. The batteries are 12 volt interstate deep cycle .  When asked about an extended warranty for batteries they tell you straight up bring them back before the one year dead line. They give you a full refund and you go back in and buy new. It costs Costco nothing as the manufacture takes them back. As the tech pointed out. He has never seen deep cycle batteries that hadn’t lost some reserve within that year.

Sorry it took me so long to reply, I don’t get on here every day. Being retired I’m so busy I wonder how I ever had time to have a job. 

I buy my batteries at Costco. When asked about an extended warranty for batteries they tell you straight up bring them back before the one year dead line. They give you a full refund and you go back in and buy new. It costs Costco nothing as the manufacture takes them back. As the tech pointed out. He has never seen deep cycle batteries that hadn’t lost some reserve within that year.

Ok!  Guess thats the way they roll.  Be interested to see the testing process the Tech puts the batteries through.

I would wonder if you really get 'brand new' batteries back. If this is standard operating procedure for them to tell people to do this, and the batteries are going back to the manufacturer... they probably get cleaned, tested, and put back into circulation. Or the manufacturer is cutting corners in many other places to allow for returns.  Nobody rides for free... and sh*t rolls downhill.

The paragraph above is personal conjecture and opinion, NOT fact. Hypothetical musings.  Just my .02, and hardly worth that to most.   

Volkemon..   you don’t swap them out. You take the batteries to the return desk just like you would a jar of pickles you didn’t like or a shirt that doesn’t fit right. They refund your money and you go shop, be it to go buy new batteries or spend the money on something else.  So if I go buy new batteries I’m pulling them off the shelf same as anyone else.  They can’t sell them as remanufactured unless they list them as such.  The brand they sell is interstate. I’m guessing they are up to par with most brands.

Keep in mind this is their policy, nothing mischievous on my end. IE; I bought a thousand dollar BBQ drop in with their so called 99 year warranty. I’d had it for 5 + years and the igniters started going out. I looked up the part number and took the igniters in to obtain new ones even if they weren’t covered under the warranty. Their response was I needed to return the entire unit for a full refund. I told them I like the unit, I just need new igniters and was willing to pay for them.  Nope, I had to return the BBQ and they gave me back all my money, even after over 5 years of use. I went back in the store bought the replacement which had some nice upgrades over my old one and cost me the exact same amount.  Also I had moved since I had purchased the original bbq so I was returning it to a diff store 125 miles from where I purchased it.


Costco makes out fine as well, it’s the manufacture that takes it back and being I live within a mile of a Costco I spend thousands there every year not counting gas which is the cheapest around and they give you 4 cents off per gallon using their credit card. I pay every month so never any interest and they give cash back the end of every year for other purchase. I typically get 450 to 600 back every year on items I always buy anyway.


Now when a manufacture sets up shop thru Costco they know the return policy. They also know their sales go thru the roof and the amount of returns is so minimal that they make bank.  Companies stand in line to have Costco sell their products. How do I know this, I know some people in companies that sell to Costco.

Free batteries??? ? We are lucky everyone doesn't think that way.

Dyna, so your saying I’m doing something wrong by accepting what they push?  I suppose you turn down free refills at your local resturant or mc Donald’s even though it cuts into their bottom line as well.  To each their own.

Do you buy from Amazon?   I do , even knowing they strong arm their suppliers into making smaller margins and taking returns as well.  Just like Costco.