12v batteries

[Captain Kidd]

My deep cycle battery is dead. I hate to pay $100+ if not necessary.

Would something like this, a 12v 7.5ah battery suffice to have on board for attaching a 12v outlet for keeping our phones charged for 4 days? And possibly running an interior cabin light for a few hours a night?

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(I realize I'm showing my ignorance of electricity)

[Spot]

The short answer is no, with 7.5 Ah that is 1.88 Ah/day which is maybe 20 minutes charging for each phone and a little left for the lights each day.

I would recommend a bigger battery and a solar panel with a charge controller.

I have had a 50w panel and controller on my boat for maybe 5 years and have been pleased with it. I just upgraded from a lawn mower to a bigger battery in anticipation of running a small Garmin chart plotter/fish finder during the day and a fan in the cabin at night. Those together consume over 15 Ah per day. My solar can make about 20 Ah on a good day so I can 'keep up' so to speak.

For a deeper dive you'll want an energy budget spreadsheet. I started here: https://www.vanlifeoutfitters.com/sizing-your-electrical-system-load-calculations/

[Charles Brennan]

Dale, The actual math is even worse than what Spot told you.   
Those A/Hr ratings are based on best rate of discharge over a 20 hour period (at room temp and sea level) from fully charged to fully discharged.  That's how the manufacturers size these things for comparative purposes.
So 7.5 A/Hr over 20 hours means to the battery maker, that the most you could hope for from the battery is .375 Amps or 3/8ths of an Amp per hour for each of the 20 hours, at which time the battery would be dead.
To be sure, you could draw MORE than 3/8 Amps, but the rate of discharge goes up exponentially.  For example, if you doubled the rate to 3/4 Amps would you now have 10 hours of battery life? 
Nope.
More like 6 hours. 
Double it again to 1½ Amps. Would you have 5 hours? Nope.
Try 2-3 hours, max.

Starting to get a feel for the numbers?
Here's another number: 2½ Amps.
That's the average current consumption of the fast-charge type newer phone chargers.
The glacially slow chargers only draw ½ an Amp.
Which is still more than the optimum discharge rate of .375A of your 7.5 A/Hr battery.
Don't forget that the slower charger has a longer charging time.
How long?   
6 to 10 hours, depending on whether you're talking iPhone or Android, and how recent the model is.
I could do some more arithmetic if ya want, but the upshot is, a fast charger gets you 2 charges before it's shot and a slow charger also gets you 2 charges, but spread over two days, before it too, is shot.
4 days use isn't even a distant dream. 

Notice, we didn't even bother to add in the LED cabin lighting you mentioned.
They range from 100 ma (.1 Amp) to 180 ma. (.18 A) per lamp.
"A few hours a night?"
Sure.
If you don't charge any phones! 

The reason that 7.5 A/Hr battery is so common and so inexpensive, is because it was designed for the burglar alarm panel industry and designed to keep an alarm panel working for at least one hour, after power failure.

All is not hopeless, however.
Your biggest problem is that you selected lead-acid gel-cell technology.
How last Millennium! 

Try something like this:
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https://www.stealthangelsurvival.com/products/portable-10-000mah-waterproof-shockproof-solar-dual-usb-charger-and-led-light?variant=44252689353&currency=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&gad_source=1&gclid=CjwKCAjwxY-3BhAuEiwAu7Y6syw0_TehGnviYWLWSS1K1EhOSYCnfTDUhmRVELts-fluIzsu_hNybhoCoJEQAvD_BwE

Don't let the 10,000 ma/Hr number dazzle you; it's just a 10 A/Hr battery, 1/3rd bigger than your example.
Also has something else going for it.
Lithium batteries keep their output voltage higher, until nearly completely drained. 
Not so with your lead-acid gel-cell battery.
Why did I cite only 2 charges on it, earlier? 
Because the voltage drop as it discharges, will trigger the smart phone charger circuitry into cutting out and turning off, even though there might still be some energy left in the battery.

The gadget I showed you also has a small LED light that you can use for your cabin lighting and it has a (too small, IMHO) solar panel to help replenish battery drain and it can go longer, before the battery is fully discharged.

Hope this helps,
Charles Brennan

[rfrance0718]

So, I'm looking at batteries as well, but for my camper. For my boat, with advice from Charles, I went with a 50 ah battery with 50 w solar panel and charge controller. I do all of the above and also run an auto helm, and a chart plotter. Works perfectly.

I went with similar setup for my camper but went with a 100 w solar panel since it's used in the winter.

Now I've decided that my 3 way fridge is never going to run reliably on propane and I want to use the 12 v option. I'm looking at a 150 ah lithium battery and a matching controller.

I can't find the specs but someone posted that the fridge draws 60 to 100 amps over 24 hours. This makes sense to me as I know that it drains the fully charged 50 ah battery down to 11.7 volts in 3 or 4 hours. I've also read that lithiums can be drained down to 20% of their charge, so longer use even if I went to a 50 ah lithium.

Other than the fridge, I charge phones and a speaker, maybe use the inverter to charge a laptop, and run led lights.

Thoughts? I've thought of buying a 100 ah battery and then adding a second if I come up short.

Thoughts?

[Captain Kidd]

Some quick responses. Thanks!

Got me answer - NO! I was suspicious. That's why I asked.

Charles, I like your suggestion. Think I'll order one. I believe that would be perfect for the CIY as well. I'm not interested in a lot of electronic gadgets. So phone charging is about all I need. I do have a portable charger that will do my phone probably 3 times. But I'll have a second phone on board with crew. I can do without the lights and go with portable LED lanterns which I have on hand. We may even do a night or two in a marina which would give us electric for the night.

Trip is 3 weeks away.

[Riley Smith]

I ordered two of these and they're bright (VERY), last a long time, have four modes (Bright, half power, dim and flashing), would make perfect interior lights, and are rechargeable. They've got a magnet base and are cheap. Perfect for what you want. This one says 4 hours on reduced light, which is enough to see with. Doesn't mention magnetic base though. Does say waterproof which is where mine died when I went in the pool with it in my pocket. Anyway these are cheap and very useful at $10 for a pair. If you order find one with the magnetic base. Has a carabiner that can clip right to your PFD. I was impressed.

https://www.amazon.com/Flashlight-Keychain-Multifunctional-Flashlights-Lanterna%EF%BC%882/dp/B0C2YT6MZL/ref=sr_1_24?crid=Z743IMT6527&dib=eyJ2IjoiMSJ9.HVtHzOcXebulmLJL85vbmKORfRKLBYS4AJp1H40fCTXo9847LNO594bG8AXMl2ukO8-cfz8s19qcwvJbOqBP1FMr7zqUwNapcrHPt880CUEY5DKUhnS3MivrSNDIpaZ_C0oqmTmyBJtWhCLMw5TCFfsG2h1DqeRi_C-uS9BrTLaRDAZOvbMwMmZH1QdFm2Ye_5dslAjjrwowfgh5TLgTPsqqrXYlX6U0S5VPj2UP6Gk6l9bqpfw2QXofs9EDa9meGgCNVEAt6wD5bIZvJudfY0SJT8A2MBUiqZzIzFZP9QY.OlmvQLqNJ9QLLK0chjyvYSi-3F0X4ljkwlJkyQjFPZY&dib_tag=se&keywords=rechargeable+led+carabiner+lights&qid=1726270488&sprefix=rechargeable+led+carabiner+lights%2Caps%2C156&sr=8-24

[Charles Brennan]

Dale, One of the challenges of our high-tech age, is learning to efficiently exploit the more subtle characteristics of our toys.

You mentioned having two phones that need a charge and also having a portable charger.
Not to get too far into the technological weeds here, but if you bring a USB cable to go from your future battery gadget to your existing charger (basically a USB-A to micro-USB cable) then by leaving the new gadget on the seat all day (or lashed to a companionway hatch, or whatever) you could keep BOTH devices at the ready. 

The solar charging replenishing capability is just about the same as the trickle charge required to replenish the portable charger.  Which is to say that as fast as the portable charger is sucking juice from the solar-powered charger is only a little more than what the solar panel is doing to keep the pack topped off.
Then, by sundown, you'd have TWO devices ready to power what toys you brought along.

I also laud your resource distribution, using discrete LED lanterns.
I ran Urchin on a single lead-acid deep discharge marine battery powering a trolling motor, for three years.  I was LOATHE to run anything else off the marine battery, because I might need those extra watts to make it the last little way back to the ramp.  Accordingly, my VHF and GPS and Depth sounder and flashlights, all had their own batteries. And I changed all my nav lights to LEDs as fast  as the technology became available.

I'll be doing the same thing on the SCAMP, since I'll be back to using a trolling motor again, although this time, I'll be using much more advanced technology (lithium batteries, MPPT controllers, etc.) than was available to me back in the mid '80's.

Hope this helps,
Charles Brennan

[Charles Brennan]

rfrance, I LOVE when somebody gives me NUMBERS!!   
As we all know:
"If You Can Put A Number On It, it's Science; If You CAN'T Put A Number On It, It's VooDoo!"   

So I took the numbers you posited:
" . . . . the fridge draws 60 to 100 amps over 24 hours."
OK, taking those two numbers, 60 Amps over 24 hours is an average current draw of 2.5 A per hour; 100 Amps over 24 hours is an average current draw of roughly 4 A per hour.

"This makes sense to me as I know that it drains the fully charged 50 ah battery down to 11.7 volts in 3 or 4 hours."
A 50 A/Hr battery has it's most efficient discharge rate at 2.5 A per hour, so if it WAS 2.5 A (60 Amps over 24 hours) then it SHOULD have gone for at least 20 hours, and not "3 or 4 hours".
You got "3 or 4 hours" so, depending on the particular battery discharge curve for a given battery, the current draw would be much closer to 4 A than 2.5 A and would more closely match your discharge measurements.

Clearly, a 100 A/Hr battery could provide 5 A per hour for 20 hours and you should be fine, except for one rub:
Your fridge runs 24 hours, not 20 hours. 
This would necessitate something closer to a 150A/Hr battery.
If it was me, I think I'd still go with  a 100 A/Hr battery and mitigate the excessive current draw with a hefty solar panel, probably 150 watts or so, keeping your battery topped off enough to get through the night (no solar!) and replenish it during the day.

I am very close to the same general current draw requirements you cite, with my trolling motor and other electrical appliances on board my SCAMP project.   I will be using two 50 A/Hr batteries in parallel and a 100 watt solar array and charge controller and I think I will be pretty close to self-sustaining.  If I fall short of the mark, my two choices will be to move to a 150 watt solar array or move to a 150 A/Hr battery (one more 50 A/Hr in parallel; the batteries I anticipate using can accommodate up to 4 in parallel) to get me the same power freedom I currently enjoy on Urchin. These benefits are all due to the improvements in lithium battery technology; using lead-acid would be far tougher, due to lead-acid replenishment times versus lithium, etc.

Hope this helps,
Charles Brennan

[Captain Kidd]

I ordered two of these and they're bright (VERY), last a long time, have four modes (Bright, half power, dim and flashing), would make perfect interior lights, and are rechargeable. They've got a magnet base and are cheap. Perfect for what you want. This one says 4 hours on reduced light, which is enough to see with. Doesn't mention magnetic base though. Does say waterproof which is where mine died when I went in the pool with it in my pocket. Anyway these are cheap and very useful at $10 for a pair. If you order find one with the magnetic base. Has a carabiner that can clip right to your PFD. I was impressed.

Saved to my wish list. I have one similar that was a gift. I'll be taking it along. Thanks for the tip!

[rfrance0718]

Thanks Charles - 50 ah batteries would fit best in my space. I think I'll order 2 of those and the controller. Then I can add a 3rd battery if needed and add another solar panel if that's needed. This should be a great upgrade.

The other issue with my camper is the door. It seals up well enough to keep water out of the interior, but not well enough to keep the plywood laminate dry. A good buddy of mine, a builder, has been scrounging things for me. He's come up with plastic sheet to replace the plywood on the inside of the door, is looking for sheet metal for the outside. He also found a really beefy continuous hinge to replace the 2 regular hinges, and a large drip edge for over the door. (the hinge was $200.00 but he got it for $50) I'm fixing up the door frame issues and I'm going to wrap the top, and sides with glass cloth. I had already wrapped the threshold.

Ski season is coming. I hope we actually have winter weather this year!