Battery Advice

Razed11 · May 2017

I'm working on system that is powered by a battery charged by solar using a PWM charge controller. To date, for our deployments in the US, we use 12 V deep-discharge (~90 Ah) lead acid batteries (to keep cost low). These are vented but do not allow for the addition of water. Now we are discussing a large deployment in South America and will have to source the battery in those countries.

While I've been enjoying learning about battery performance I am far from expert. Ideally what I'd like to do is evaluate a few batteries by measuring their charge profile and discharge down to the load disconnect voltage of the charge controller. But I'm wondering if the battery I buy here will be the same design as the one purchased there (that might sound somewhat paranoid). Trojan batteries seem to have a good reputation but can be expensive. My current budget is around $90 and, of course, I'm being asked to reduce that cost if possible.

It doesn't seem to me that it would be difficult to manufacture a reasonable quality battery of this type but I also know that corners will be cut.

Can anyone recommend a reliable manufacturer that can be found internationally?

What traits should I look for in these batteries?

If not all batteries of this sort are equal what things are sacrificed to keep manufacturing costs low?

Thanks for read.

mvas · May 2017

Razed11 said:

.... To date, for our deployments in the US, we use 12 V deep-discharge (~90 Ah) lead acid batteries (to keep cost low). These are vented but do not allow for the addition of water ...

Are you talking about AGM Batteries?

Razed11 said:

If not all batteries of this sort are equal what things are sacrificed to keep manufacturing costs low?

Quality, Reliability, Capacity, Cycles, etc ...

Razed11 said:

Can anyone recommend a reliable manufacturer that can be found internationally?

Lifeline, Trojan & Vmax make a reliable AGM battery.

Razed11 said:

My current budget is around $90 and, of course, I'm being asked to reduce that cost if possible.

You want a quality 12 Volt 90AH Deep Cycle AGM battery, for less than $90?

Razed11 · May 2017

Sorry. Not AGM. Flooded batteries.

Regarding the manufacturing: Very often, especially for the cheaper batteries, it is difficult to find specs and even then I'm not sure if I can believe them (hence why I'd like to perform some measurements). What should I look out for from a construction standpoint? Though I suspect the only way I'll learn that is by dissecting it.

mvas · May 2017

OK, flooded allows water to be added.
There are the "top tier" flooded battery manufacturers and
then all other Branded batteries are just re-labelled batteries from 4 manufacturers.

Crown 12 Volt 95 AH = $138
https://www.solar-electric.com/repoba12vo95.html

Estragon · May 2017

You can load test for capacity, but you'd really have to cut a bunch of them open to get a sense of consistent quality control in manufacturing. US Battery sells worldwide through distributors and likely has reasonable QC. I've found price decent in Canada compared to Trojan etc. I imagine freight would be a significant factor.

I personally wouldn't buy a flooded battery that can't be watered.

Dcmike · May 2017

cost will determine where you live where i live i got cr235 crowns for 105$ each but they are 6 volts they are doing very well, they seem to have the same ah's as they did 3 years ago when i bought them

Razed11 · May 2017

Thanks.

I was told by a member of my team that the battery vented but did not have a way to add water (I had specifically asked about maintenance). I work remotely from that team and may have been misinformed.

Do you think these caps can be removed for the addition of water? It looks to me like there is a lip to pop them off. This is an $80 battery.

Image: https://us.v-cdn.net/6024911/uploads/editor/ly/wmbd3qhpe2ll.png

littleharbor2 · May 2017

Looks like a typical flooded lead acid battery. The caps are removable. Not sure what lip you are referring to but the entire cap comes off. You would pry up from under the cap flush with the top of the battery case.

mvas · May 2017

Sorry, that is not a true Deep Cycle battery.
It just has label that says "Deep Cycle" - ( a cruel joke by the manufacturer ! )
It is a Marine Hybrid, a dual purpose Starting & Trolling Motor battery with very limited true deep cycles.
It is a bad compromise, it is neither the best starting battery nor the best deep cycle battery.

mvas · May 2017

Better Deep Cycle is ... two Golf Cart GC2's in series or one GC12 ?

Estragon · May 2017

More likely to find 12v in the 90ah range at a decent price I would think. 2xGC2 6v would be ~225ah.

That does look like a flooded, waterable battery. Maybe your team member was concerned about uninformed end users adding tap water (should be distilled)?

Razed11 · May 2017

The "cruel joke" is exactly the kind of thing I am concerned about. The current configuration has a 100 W panel and seems to keep things topped off but it takes up a lot of space that our client is objecting too. Now that I'm looking at smaller panels our not-so-deep-discharge battery may quickly become the weak link depending on the number of a cloudy days.

I don't need cranking amps--our system consistently pulls about 325 mA at 12 V--but uptime is important and these systems are designed to be left alone for a year or more.

The GC batteries would be a dream from a capacity standpoint but I don't think the budget will allow them.

I appreciate the education and the practical input from everyone that has commented.

BB. · May 2017

Many of those types of marine/car batteries are designed (additives to the plates) to release very little water/hydrogen/oxygen. As long as they are not charged at a very high voltage (typically around 14.0 to 14.2 volts or so, and down to ~13.6 volts for "float")..

If you have a "cheap charger" or charge to (what is standard for a flooded cell deep cycle battery) ~14.75 volts (and hold for hours/days/weeks), even these "maintenance free" batteries will need to have distilled water added (had that problem with a car my in-laws hardly drive--Got a "cheap" charging cube (says for float charging)--But I would need to refill the battery every ~6 months or so (driving, never had to fill the battery).

Got a better "float charger" (Battery Minder or Battery Tender are two US brands that work well), and had no further problems with water loss.

You did not say much about the application. How many Amp*Hours per day are you pulling from the battery? Will these be "floating" (15% maximum discharge) or "deep cycling" (~25% to 50% cycling every few days)? High temperatures in the room/cabinet)?

What are your expectations (replace batteries every two years, every 5 years, complete R&R of system every 8 years, etc.)?

If maintenance is an issue--AGM type batteries may be a better solution. No water to add, very low self discharge, very clean. Down side is ~2x higher costs (vs flooded cell) and, in my humble opinion, a couple years less life than a (well maintained) similar quality flooded cell.

Other battery chemistries may also be "interesting" too--Again depending on your needs.

-Bill

Estragon · May 2017

On the panel size thing, there are some that get better than the 16% or so efficiency typical of mass market. Unfortunately without a NASA type budget, probably not viable.

Assuming the .3a load is pretty consistent, the 90ah battery should give you ~5 days autonomy to 50% SOC. Does South America where this would be deployed have a rainy season where it can be cloudy for weeks at a time? If deploying in the higher latitudes, will the panel tilt be set for lower sun and maybe snow shedding if higher altitudes?

bsolar · May 2017

for sub 90 buck batteries i wouldnt worry too much about it, testing ect .. theyre basically disposable .. watch dumping them deep and keep a close eye on balance if you want them to last a year ...

Razed11 · May 2017

BB. said:

Many of those types of marine/car batteries are designed (additives to the plates) to release very little water/hydrogen/oxygen. As long as they are not charged at a very high voltage (typically around 14.0 to 14.2 volts or so, and down to ~13.6 volts for "float")..

If you have a "cheap charger" or charge to (what is standard for a flooded cell deep cycle battery) ~14.75 volts (and hold for hours/days/weeks), even these "maintenance free" batteries will need to have distilled water added (had that problem with a car my in-laws hardly drive--Got a "cheap" charging cube (says for float charging)--But I would need to refill the battery every ~6 months or so (driving, never had to fill the battery).

Got a better "float charger" (Battery Minder or Battery Tender are two US brands that work well), and had no further problems with water loss.

You did not say much about the application. How many Amp*Hours per day are you pulling from the battery? Will these be "floating" (15% maximum discharge) or "deep cycling" (~25% to 50% cycling every few days)? High temperatures in the room/cabinet)?

What are your expectations (replace batteries every two years, every 5 years, complete R&R of system every 8 years, etc.)?

If maintenance is an issue--AGM type batteries may be a better solution. No water to add, very low self discharge, very clean. Down side is ~2x higher costs (vs flooded cell) and, in my humble opinion, a couple years less life than a (well maintained) similar quality flooded cell.

Other battery chemistries may also be "interesting" too--Again depending on your needs.

-Bill

We have a Morningstar PWM based Sunsaver as a charge controller and I have access to the battery voltage data for every station. Very often you see the charge controller kick on in the morning, bulk charge until 10-11, move to constant voltage mode (absorption) for about three hours (the Morningstar uses time rather than current monitoring), then it moves to float. The charger supports sealed or flooded batteries using a jumper and has some temperature compensation. It does have an equalization mode that runs every 28 days. It seems to me that charging is working well and at proper voltages.

The expectations for battery replacement are still being worked out. Obviously there is a trade-off between sending someone out to do maintenance and having a battery that doesn't require it.

I saw this AGM battery for $91. It has a 50 Ah rating at 20 hours or a 2.5 A discharge current (if I'm interpreting this correctly). Since we are pulling a fairly consistent 0.350 A it seems that we might do much better than this in capacity.

Razed11 · May 2017

Estragon said:

On the panel size thing, there are some that get better than the 16% or so efficiency typical of mass market. Unfortunately without a NASA type budget, probably not viable.

Assuming the .3a load is pretty consistent, the 90ah battery should give you ~5 days autonomy to 50% SOC. Does South America where this would be deployed have a rainy season where it can be cloudy for weeks at a time? If deploying in the higher latitudes, will the panel tilt be set for lower sun and maybe snow shedding if higher altitudes?

I hunted around a little for a panel that was closer to 20 % but didn't dig too deeply as I'm working around this Renogy 50 W (to drive one stake in the ground) since we have some good history with the 100 W panel by the same vendor. The 50 W shipped to my house for like $90. The panel will be at a fixed tilt in the field.

My next big task is to attempt to estimate how much energy I can harvest in the specific locations in South America. There is some SUNY model data for one location that I hope to use. This is really the trickiest part and haven't yet tried to crunch the numbers.

Estragon · May 2017

A 50ah battery gets you down to 2-3 days or so of autonomy (assuming 24hr load) to 50% state of charge. In an unattended remote system with no backup charging being deployed (I assume) in places with varying weather, this might be cutting it a bit fine. You would have to decide whether to have the controller disconnect the load to protect the battery, in which case it goes dark, or let the battery run down more, and risk permanent loss of capacity.

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