Good "cheap" AGM Battery

[VanLifeCrisis]

Wondering what 12V AGM battery would you guys recommend for a 200 watt solar setup. Also, will one fit in a 12"W x 13"H x 20"L box? (with clearance for the posts)

 

[MikeRuth]

You can start here using this site to get comparisons on batteries and all the dimensional information.
http://www.batterystuff.com/batteries/rv-marine/agm/#a8817

AGM batteries typically are more expensive per Amp Hour than a flooded battery.

 

[Seraphim]

I think the first question is how much capacity - in amp hours - are you needing? Or are you just going for the most you can get?

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http://www.batterystuff.com/kb/tools/bci-battery-group-sizes.html


Above is a size chart for batteries. It also has links to a couple of manufacturers by size. If you can go to 20.5" somehow, the 4D appears to be the largest you can go in a 12v. 200AH

Might get more AH with (2) 6v to fit in that space, but it won't be cheaper.

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If the chart is correct, you might get 3 type 31 batteries in that space - for 375 amps. I'd double check those dimensions though.

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4Ds AGM look to be about $550. Type 31 Agm about $350.

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Check weights on the larger size batteries as well as dimension.

 

[Almost There]

Thanks for the charts, this info is on the 'to find out' list for me.

Is it better to get, say, 2 - 100 amp batteries than to use 1 - 200 amp battery if space is not an issue?

 

[Seraphim]

I don't know about 'better' - a quick guess, one 200AH battery is probably cheaper than two 100AH batteries and take up less room. Slightly easier to install just one. Probably weighs less, as well. It pretty much depends on what's important to you.

We found the best combination of AGMs for our space was four GC2 6v batteries which give us at least 420 AH. Haven't gotten them yet, because the total cost IIRC would be about $1000. Using flooded cells, and the large battery cases needed for venting fumes, the best we could do was two type 27 in the same space, for 210AH. Only cost about $300, though.

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We already had the battery cases though, so we didn't have to buy them. If you go flooded cell batteries, make sure to include those in the price estimate.

 

[AuricTech]

All else being equal, I would prefer one 200Ah battery over two 100Ah batteries. No parallel connections to go wrong.

For a 200W PV array, I would go with a battery bank of about 100Ah, unless you have some other source of charging current. Here's the calculation that shows why (it's a formula I got from one of the moderators over at the Northern Arizona Wind & Sun forum):

(.77 derating factor * 200W PV array) / (14.5V charging Voltage * .1 charge rate) = 106Ah battery bank

 

[Almost There]

Thanks Aurictech, I haven't even started working on the plan for where all the equipment is going, what I need, how much power I'm going to consume etc. etc. ad nauseum but every little bit of information helps.

The reason I was curious about 1 battery or 2 is because there's a price difference between those choices but I'd rather pay upfront than repeatedly.

 

[ccbreder]

Check the weight of one 200 amp battery against the weight of a six volt battery. I would rather move and install multiple small batteries than one super heavy single battery. Properly made connections are required anyway and will not be a problem.

 

[Almost There]

Check the weight of one 200 amp battery against the weight of a six volt battery. I would rather move and install multiple small batteries than one super heavy single battery. Properly made connections are required anyway and will not be a problem.

You've got a point there. I can probably arm-wrestle a 6 V battery but even a regular 12V, if it's got to be moved an awkward way like sideways or lifted over the edge, is likely to be a 'someone come help me' moment! Hey, I'm a senior and not an athlete...

 

[SternWake]

While it depends on the amount of other charging sources, I think the biggest consideration is not fitting in more capacity, but more matching the battery capacity with the Solar so that the battery sees at least X amount of amps at high noon on a sunny day.

While any solar is better than no solar, too little solar for too much battery will also cause premature battery failure.

My group31 USbattery is rated at 130 amp hours.

USbattery recommends a 10% rate, which would be 13 amps.

My 200 watts of solar can do 13 amps, on June 21 at noon at 33'N, and this battery is retaining more capacity and performing well, despite being cycled deeper than the 2 group 27's I used to have in parallel as a house bank.

When cost to amp hour is compared, I will be spending less money when this single battery needs replacement, compared to when the 2 27's would have needed replacement. The difference I averaged ~2.2 years+ with 2 27's, and am now at 13 months with the single group 31, and estimate i have about 3 to 4 more months before its capacity is too small to meet my overnight needs, when I am being wasteful. So spend 250$ every 27 months, or 130 every 15 months, and carry around 62 less Lbs, in my case.

So while the 1 watt for every amp hour of storage is a general rule, I feel it is way low to keep a daily cycled battery healthy for the long haul, and I think too many people put importance on maximizing capacity instead of maximizing recharging ability. The more capacity one has, the more current one should have to recharge them. it is not just a matter of replacing the amp hours used + ~10%, it is meeting some basic minimum recharge rate, so that the solar, on a good day, can get the batteries upto acceptance voltage before noon, and has the time it needs to get the battery upto maximum Specific gravity and the elusive but necessary 100% recharge that All lead acid batteries require every so many cycles, to live a respectable lifespan.

As for an Acceptable AGM, a low dollar one, the Sears Die hard Gold is a rebadged Deka intimidator series, and a group 27 runs about 180$.

High $ AGM like Odyssey and Lifeline and Northstar really require Large charging currents when deeply cycled, and as such do not make good solar batteries.

A hundred amp hour Odyssey/ sears die hard Platinum requires a minimum of 40 amps of charging current when deeply cycled, and will not behave well when 200 watts of solar are the main recharging source.

But, if the vehicle is driven first thing in the morning, for a half hour, and the alternator charging circuit is thick, then well over 40 amps can flow into such a battery, and quench that high amp desire that these High$ AGM batteries have, and then 200 watts is acceptable if it can get the battery to 14.7v and hold it there for 4 hours every day..

But shorter drives, thin alternator copper cabling and 200 watts in west virginia will degrade such an AGM quickly.

Do note the high alternator amps are highly beneficial to all batteries when they are cycled nightly. I've noticed over the years that all my batteries simply behave much better the next discharge cycle when I drive in the morning first thing and feed it/them 70 to 90 amps, and let the solar take over.

But I still employ a grid powered charging source, because I dont always drive enough, and I dont always get enough sun, and I do not like going days with a battery hovering below 80% charged.

 

[VanLifeCrisis]

thanks very much for the info. i was thinking a single, smaller capacity battery might be better.