# Battery Recommendation



## MoonRiver (Sep 2, 2007)

I have a 45 watt harbor Freight solar setup (3 panels, controller, inverter) I'm not using. I just bought a 10' x 10' tent to use along with my 14' fiberglass travel trailer.

I need an inexpensive and safe battery. I want to just stick it in the back of my SUV and then put in the tent when I get to campsite. I'm thinking a couple of 12 v lights, recharging camera, cell, etc, and maybe a low watt appliance needing an inverter. Battery would be fully charged at home and then charged daily with solar.

My trailer has 2 deep cycle marine batteries - 12 v, group 24, 75 Ah. By buying 1 of these, I have a spare if I need it. 

Is this a good choice? Is it safe to carry inside the vehicle? Any safety precautions I need to take?

Thanks


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## wy_white_wolf (Oct 14, 2004)

The HF kits are only large enough to properly charge a 30 to 35AH battery. While they will charge one of your 75AH batteries the charge rate is not high enough to stir up the acid in the battery to prevent sulfication of the plates. It would die a slow death.

WWW


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## Peasant (May 18, 2013)

I believe the IMP (current at maximum power) for HF kits is 2.25 amps. Assuming it actually produces this, you'd want a battery around 15-25 amp hours. This would give you a charge rate around 10%.

This kit won't properly charge a bigger battery, not year round at least. A 35 ah might be OK in summer. I certainly wouldn't go any bigger than 35 ah, and would have some other way of charging it during poor solar conditions. You can get sealed 35 ah batts on Amazon for $60something shipped.

75 ah is WAY too big for this kit unless you just want to use it as a trickle charger. Charge rate would only be around 2-3%, much too low for regular use.

ETA: When transporting flooded lead acid batteries you need to make sure they don't tip over. I'd also keep them some place they can vent safely (i.e., not in the cab of your truck).

Sealed batteries are a little more forgiving, they can be transported on their sides without issue.


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## AVanarts (Jan 2, 2011)

Actually, if you leave off the inverter, it should be easy to find a small rechargeable 12 volt battery that would meet your needs. 

I have some of these 12 volt LED lights in my off grid cabin. They take very little juice to operate and give off a surprising amount of light. http://www.ebay.com/itm/350805504078?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Charging things like a phone or camera also wouldn't take that much power.

I would probably look for a "dry" type rechargeable battery, but if you want to use a RV battery, then just make sure it is charged good at home and you should only need to use the HF panels to keep it topped off.

If you run the battery down, then like the others have pointed out, the HF panels would be too small to get it charged back up.


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## MoonRiver (Sep 2, 2007)

How about this as an option.

I have a 100 watt solar panel (portable) I use to recharge the batteries in the RV. I could use it for a few hours a day on the tent battery and then switch it over to the RV batteries. Or 1 day on tent battery and 2 days on RV batteries.

Would that be a good solution? I'm getting ready to switch the RV lighting to led, so I really don't use much electricity in the RV. Fans are probably the biggest draw.


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## spacecase0 (Jul 12, 2012)

I have 300 to 600AH of aircraft AGM batteries connected to 40W of solar, took me a month to top them off with my solar, I run about 60mA (0.060A) of LED lighting at night off of it, plenty of light to see by, and the system is topped off by 9am each morning, if I were using a single 7AH worn out battery with a capacity of 3Ah and 10W of solar I would be fine. get your power usage as low as you can and you win with almost any solar power system


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## Peasant (May 18, 2013)

MoonRiver said:


> How about this as an option.
> 
> I have a 100 watt solar panel (portable) I use to recharge the batteries in the RV. I could use it for a few hours a day on the tent battery and then switch it over to the RV batteries. Or 1 day on tent battery and 2 days on RV batteries.
> 
> Would that be a good solution? I'm getting ready to switch the RV lighting to led, so I really don't use much electricity in the RV. Fans are probably the biggest draw.


Really depends on how much you draw from the batteries and what their capacity is. You said your RV batts are 75 ah each and you have two of them, presumably wired in parallel, giving you 150 ah @ 12V. If you drew these down to 50%, it would take a bare minimum of 14 hours of full sun for a 100W panel to get them back to 100% (but in reality it'd be a lot longer).

The only way to find out for sure is to monitor your batteries and your loads. You need a meter of some kind, for small applications like this a Watts Up or similar in-line meter would work fine (I'm very happy with my Watts Up meter). You can also use a Kill-A-Watt, but this is only useful for the inverter output. Your charge controller may also have meter options.

A good hydrometer (assuming you don't have sealed batteries) is a must, measuring specific gravity is the only way to really tell what your batteries' state of charge is. I'm a big fan of the Hydro-Volt, much better than cheap auto store hydrometers. Measuring resting voltage is just a proxy for state of charge, and can be hard to do if the batteries are under a near constant state of charging and discharging like mine are.

Powerpoles would be highly useful for a system like you're proposing, makes things much easier to move around and helps prevent accidental reverse polarity incidents.


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## MoonRiver (Sep 2, 2007)

Does anyone have a good source for agm deep cycle batteries? I think something between 35 and 70 Ah would work. I hate to spend $150+ for a battery when it won't be used every day.


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## wy_white_wolf (Oct 14, 2004)

I buy my batteries locally as the shipping is too much trying to get them off the internet.

WWW


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## poorboy (Apr 15, 2006)

Peasant said:


> Really depends on how much you draw from the batteries and what their capacity is. You said your RV batts are 75 ah each and you have two of them, presumably wired in parallel, giving you 150 ah @ 12V. If you drew these down to 50%, it would take a bare minimum of 14 hours of full sun for a 100W panel to get them back to 100% (but in reality it'd be a lot longer).
> 
> The only way to find out for sure is to monitor your batteries and your loads. You need a meter of some kind, for small applications like this a Watts Up or similar in-line meter would work fine (I'm very happy with my Watts Up meter). You can also use a Kill-A-Watt, but this is only useful for the inverter output. Your charge controller may also have meter options.
> 
> ...


First let me state that although I wired my own home and the co-op checked my wiring when they hooked it up and passed my work, i consider myself to still be a rank newby to solar and batteries...That said my question is"Would it be possible to simply mount automotive amp meters or meter to keep track of the charge in your batteries?"


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## topofmountain (Nov 1, 2013)

poorboy said:


> First let me state that although I wired my own home and the co-op checked my wiring when they hooked it up and passed my work, i consider myself to still be a rank newby to solar and batteries...That said my question is"Would it be possible to simply mount automotive amp meters or meter to keep track of the charge in your batteries?"


YES you can.


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## Jim-mi (May 15, 2002)

Yes you can 
BUT; 
They are inappropriate and totally inaccurate for the job........period.

A TriMetric is far and away better to tell you the energy In and Out of your battery.


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## poorboy (Apr 15, 2006)

Jim-mi said:


> Yes you can
> BUT;
> They are inappropriate and totally inaccurate for the job........period.
> 
> A TriMetric is far and away better to tell you the energy In and Out of your battery.



Don't know if I'll ever get around to going solar (my age) but i enjoy learning!


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## Peasant (May 18, 2013)

poorboy said:


> First let me state that although I wired my own home and the co-op checked my wiring when they hooked it up and passed my work, i consider myself to still be a rank newby to solar and batteries...That said my question is"Would it be possible to simply mount automotive amp meters or meter to keep track of the charge in your batteries?"


The best way to measure a battery's state of a charge is with a hydrometer, assuming you're using flooded lead acid batteries. A cheap auto-type hydrometer will work, but I prefer the Hydro-Volt (expensive, but worth it IMHO). 

If you're using sealed batteries you're limited to measuring resting voltage.

Installing a voltmeter is a good idea regardless, but voltage is only a proxy for state of charge, especially if the batteries are undergoing constant discharging and charging. Ideally the batteries shouldn't have any loads for 3+ hours to measure resting voltage, which can be difficult if you use them on a daily basis and have solar panels to charge them.

If the load/charge amperage is low enough, consider a Watts Up or similar inline meter. It shows volts, amps, amp-hours, max amps. I think the wires are only #14, so that limits you to 30 amps. I have my Watts Up between the charge controller and the battery to see the voltage and amps going from my solar panels into my batteries. I'll be replacing it soon with a Morningstar meter for my charge controller once I expand my solar array.

If all your loads go through an inverter, you can use a Kill-A-Watt. Find the watt-hours used and divide by 12 to get amps @ 12V. I use the Kill-A-Watt to measure my AC loads, then estimate inverter draw to get total amps I'm drawing from the batteries.


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