Is 100Wh from a standard Group24 battery reasonable?

[Reflex439]

I don’t know the condition or actual specs on the battery, but its a used battery in a RV I purchased used.
Here is how it is marked;
M24-1 starting marine battery
Marine cranking 625
Cold cranking 500
Reserve capacity 95

When using it, I can get a hour or so running a 19” 12V TV, running the fantastic fan on low most of the night, a couple LED lights, and the refrig on LP setting. In the morning the monitor I have installed shows ~100Wh of energy used, voltage of around 11.8 to 12.0 with a light load (refrig on LP and fan on low), and needing to be recharged.

I am not familiar with watts vs amps over a time frame, so I don’t know if 100Wh is typical for a Group 24 battery before needing to be recharged. Does this seem normal for similar batteries? If not, what might be considered more reasonable for a Group 24 deep cycle battery? 1.5x, 2x or ???

Currently this is the only house battery installed, other than the vehicle battery which is isolated. I have just enough room for two side-by-side group 24 batteries (see dimensions below).

Just looking for ideas on increasing the current capacity, and hoping for a minimum of a two fold increase. I do not want to modify the existing battery compartment, so the right solution needs to fit in a 14”W x 10.5L” x 9.5”H space

Thanks...

[Almot]

Yeah, meters are not all created equal. Different quality and different features.

You need to measure AH or WH, not amps. God knows how many hours you run fans or TV. Let the meter counts AH. A decent one will cost $30-40 on Amazon.

[MEXICOWANDERER]

IMHO excellent advice MrWizard. Some soy sauce amp hour meters use the positive side.

Food for thought for battery comparison....

Amp hours at the 100 hour rate. Difficult to find data because cheapo battery manufacturers consider this "Extraordinarily Privileged Information". Gee I wonder why? This is where the Lifeline hoses AGM competition.

High density acid skews the picture with flooded batteries. Chew and spit 1.400 acid characteristics would turn car jar cyclable batteries into real powerhouses. Complete with a ninety-day warranty. Look for it...

[MrWizard]

Reflex
It seems you wired it correctly
But a 19 inch TV that only uses 12w, seems like a miracle to me
Although the fan power seems right
There are no stray negative wires connected on the wrong side of the shunt? The only thing on the negative battery post is the shunt?
ALL negative wires are connected on the output far side of the shunt?

Any negative wire connected at the post side instead of the far side will be bypassing the shunt and NOT give a reading on the meter

[MEXICOWANDERER]

If you are looking for premium value, research Lifeline made by Concorde. They are expensive but the power / size ratio is superb. They recharge faster. And their lifespan is unparalleled. One battery of this type may do the job for you. There are other brands of AGM battery but they cannot compare with the durability of a used-hard Lifeline. Compare the cost of one Gr 24 Lifeline to a pair of Trojan's deep cycle batteries. San Diego California) Battery has good prices. AGM batteries can be shipped.

[Reflex439]

Very helpful advice. If I decide on two new batteries, yes, I’d only go with matching new batteries and treat them as a pair. Same I as do when building lithium battery packs for my giant scale RC airplanes. Installed together, they become one.

Not sure if I can go with Goup27 batteries. The space thats available to be can barely hold two Group24s side by side, with no extra space. 14”L x 10.5”W x 9.5”H. I’ll get the most capacity that will fit. I’ll take head to your warnings on manufacturers over zealous ratings 🙂 Anyone have an good recommendations on quality Group24 batteries?

Re the meter, while I would prefer it to read properly, in the end I really don’t care what it indicates. If I can calibrate it properly I will. If not its still a consistent number based on actual usage that I can then chart and as an indicator for capacity.

Much help, thanks….

red31 wrote:
while solar doesn't add capacity, its ability to FULLY charge can add capacity and keep batteries happier when not camping.

How is that any different from a decent chargers ability to FULLY charge the batteries, regardless if its from generator, shore power, or the sun? Are solar charges somewhat different from a good 4-stage charger? I thought they were just as good. What am I missing here?

[red31]

Your G24 starting battery is not for the job. Auto parts store is happy to load test, but in any event its cycle ability is limited.
compare a g24 starting battery @ 37lbs to a G24 deep cycle @ 46 lbs.

while solar doesn't add capacity, its ability to FULLY charge can add capacity and keep batteries happier when not camping.

[RJsfishin]

You have set the maximum limit on battery storage capacity by stating that your battery box will hold 2 group 24 batteries, and that you are not going to modify it.

If you stay w/ 2 12v batteries, your maximum usable capacity is 80 amp hrs, or 960 watt hrs.

if you have the height for 2" taller batteries, then you can go w/ 2 6v golf car batteries, which will have a useable capacity of 115 amp hrs, or 1380 watt hrs.

Is that by any chance the information you are after ??

Having said that, that would increase your current capacity 13 times ???

[MEXICOWANDERER]

The meter itself is suspect. Anyway look at it this way...

The existing battery cannot do the job

Regardless never pair a brand new battery with an old battery.

Time to get 200 A/H worth of batteries then start playing with the meter. A correct 50% discharge level for a 80 amp hour battery 40. ¿Si?

40 X 12.2 volts the span average I use is .488 kWh consumed. 1 hour 90 days, the consumption is .488 kWh

You may or may not want to trade kWh potential for overall lifespan + ease of deep cycle maintenance). Golf car GC220 batteries fall under the latter category.

As battery specs get more crooked and deceptive, plates get thinner and paste less pure. Look for amp hour ratings and weight (amp hours per pound). The fewer the amp hours the thicker the plates = when comparing equal weights.

After your battery selection is made only THEN, start calculating draws and recharges. Note that batteries "cure" after ten cycles or so. You can help by performing a "TOP CHARGE right out of the box.

A DEcrease of discharge from 50% to 60% remaining capacity is something to consider. This is why I recommended 2 group 27 good quality batteries like Trojan or Deka.

Watt seconds, minutes, or hours is MOST useful in COMPARATIVE battery studies. Comparing a battery to similar ones off a production line - comparing current energy factors to the battery when new.

Little value in hitching a fresh horse to a 2 horse wagon when the other horse has a broken leg.

But in any event replace with 2 new batteries. Is this recommendation redundant enough?

[Reflex439]

The battery monitor shows the following;

TV runs about 1A
Fantastic Fan on low, 1A
2 LED lights show .32A
Everything off except detectors, refrig on LP, phantom draws, etc show about .10A to .12A draw.

A typical day might be an hour on the TV, 3-4 hours on the fan, and 2 LED lights for about 4 hours. Of course the refrig on LP and detectors on 24x7.

Meter shunt is installed directly on the negative post of the battery, as the instructions dictated, diagram below.

Fred, I plan on solar down the road, but solar does nothing regarding total capacity which is what I’m trying to address. Once I get this resolved, I have two 100W panels planned for the RV. Although not as handy for me as they don’t work all that well in the shade, which is where I prefer to park for cooling reasons.

[MrWizard]

That's 35 amp hrs per 24 hours
17.5 ah from 8pm to 8am
And does not include TV and fan etc...

100 watt hrs over night does not compute anywhere near normal usage
We can't confirm a bad battery until we can verify the usage and the meter install, please give more info about the location of the shunt
And how much power draw it shows when items are being used

Example...I have new AGM batteries
My power meter showed 12.9v at 11:30 pm when I went to bed
At 6:30am (very early for me) It was down 13 percent, battery capacity remaining 87.2 percent
Voltage reading 12.75

Your meter says you used 100 wh , approx 10 percent of what that battery should have when new
Yet your voltage 11.9~12.0v indicates 50 percent charge or less
Flooded cell and AGM do have different voltage curves, but you get the idea, a 10 percent use should have a much higher voltage reading than what you show

A: battery is toast
B: something wrong with meter or installation
C: battery not fully and completely charged before using

This is where the amps function comes in to play
If and when you can see 14.? Volts and only 1 amp or less charging current then the battery is full
A battery still accepting 4 amps at 13.? Volts is not fully charged
Most batteries die from sulfation on the plates, gradually losing capacity from not being completely and fully recharged

[Golden_HVAC]

My E-meter has a accurate reading, so I can tell how much power I am using from my 4 golf cart batteries.

Your refrigerator, CO meter and propane detector all together consume about 35 AH per day, or about 35X12volts or 420 watts. This is about what one of my 120 watt solar panels will put out in a day in the sun.

I would recommend a pair of solar panels in the 100 - 150 watt size range. Then you will be able to dry camp for a couple of days, or a week (without needing the furnace), and still have plenty of power.

SunElec.com

They are fairly easy to install.

Fred.

[DrewE]

It sounds to me like the battery is toast, or very nearly toast. 100 Wh is not much. The battery in my laptop (well, technically it's my employer's laptop) is rated at 94 Wh. The one in my cordless drill right now is rated for 72 Wh. Admittedly, in both cases, they're on the larger side of batteries for those applications, but still....

Watts are computed by multiplying volts time amps. Watt-hours are computed by multiplying volts times amp-hours.

[Almot]

Reflex439 wrote:
I thought it might be a cheap battery, but wasn't sure. So a 200 amp hour total capacity should get me 200Wh before needing recharge?

Er... No.

Cheap is cheap, AH is AH, and 200 AH battery in a good shape will give you about 1,300 WH before needing a recharge.

What you need is a "deep cycle battery". The one that has capacity rated in AH.

A single 200 AH 12V deep cycle battery will need a crane to lift it. Normally people buy 2*100 AH. Or a pair of 6V golf cart batteries for total 225 AH.

1AH = 1WH/13V.

Battery should better be recharged before it drops to 40-50% of capacity.

Your old Group 24 is not rated in AH or WH because it is not intended for slow discharge. Roughly, it "was" about 80 AH = 1,000 WH capacity with 500 WH usable capacity when it "was" in a good shape. Right now - hard to tell.

[MrWizard]

1 amp at 12v is 12 Watts , 1 amp for 1 hour is 1 amp Hr aka 12 Watt hrs

Yes 12v after 100 watt hours of use is a bad battery
That should be an 80 amp hour aka 960 watt hour total capacity battery with 400 watt hrs usable

But 100 Watt hours use is fantastically low, that's everything turned off except for maybe the fridge controls
No lights no TV no water pump.. Absolutely nothing

The usage in your OP would account for more than that
What is the amps draw on the meter with the TV and fantastic fan and LED lights on while watching TV
I think the meter is out of calibration or not in line with all power drain

[red31]

100 wh from a 1000 wh battery and it below 12v, I'd suggest the condition of the battery is poor.