I'm pretty sure my new battery from last summer is dead because of my negligence. So, it's time for me to do some learning and make some decisions. I've spent a few hours looking online. Some of the newer folks here might benefit from my learning curve. The battery industry seems to be full of "misleading" information, and a lot of this seems to be around marine and deep cycle batteries.
Here are some very simple basics that I have learned:
(
https://www.solar-electric.com/learn...ttery-faq.html )
A normal automobile battery primarily for starting is designed to be discharged (DOD) only about 2-5%.
True deep cycle can be discharged down to 20% (DOD = 80%), but will last longer if normally discharged to 50%, and much longer if only discharged to 20%.
Marine batteries are somewhere in between, and seem to be all over the map of the battery world.
When I search for deep cycle batteries, I seem to come across marine batteries. Apparently, many deep cycle batteries will supply enough current to start a motor. However, I have come across a few batteries that have no cranking amps specified, so I assume those are designed primarily for lower currents and would not be suitable for starting motors. The site
www.batteriesinaflash.com seems to have a wide selection, and as all research goes, raises more questions.
Many here and elsewhere swear by the Trojan T-105. It seems to be a very good battery, but you'd need two of them, and if I want to store a generator in the storage compartment, either the batteries will have to go, or the generator. That will mean relocating the batteries. I'm not against that. Trojan also sells some deep cycle 12V batteries:
J185P (12V) has virtually the same amp-hour as the T105 (6V). (T105 is slightly higher).
A typical deep cycle group 27 battery seems to have a footprint of about 7"x10". The J185P footprint is 7"x15". I'll have to check it out, but that may be cramping the storage space. It is also a couple of inches taller than most. A T-105 (6V) has a footprint of 7"x10". Because you'd need two of them, you'd be looking at a total footprint of 14"x10" or 20"x7". However, the height is roughly the same as any group 27 battery.
Cost wise, the T-105 will set you back $170x2 = $340 USD, Amazon's price in May 2019. A J185P from batteriesinaflash will set you back $360 USD. (This does not include shipping) The cost is slightly more. The J185P does not list any cranking amps, so I assume this is a true deep cycle battery.
I'm not trying to make a plug for Trojan. Rather, I'm just trying to compare apples to apples. Trojan is known to be a quality manufacture. There are others out there, but this may make a foundation with which I can compare other batteries.
Summarizing the choices from Trojan:
T105: (need 2): 217 amp hours.
10"x14" footprint
Motive 24TMX: 85 amp hours. CA not listed at Trojan or batteriesinaflash
6.5"x11" footprint.
Based on the lack of cranking amps, I will assume the plates are more solid and robust so as to not be able to provide sufficient cranking amps. However, it lacks capacity.
Motive 27TMX: 105 amp hours, $200 USD. CA = 650A (batteriesinaflash, not specified at Trojan)
6.5"x13" footprint
For its capacity, it seems to have a pretty low cranking amps so I assume this is not the best choice for starting a motor. I noticed that even Trojan did not list the spec, so this probably represents a true deep cycle battery and has robust plates. However, the footprint is getting larger.
Motive SCS150: 100 amp hours, CA = 650A (from Trojan)
7"x11" footprint
This battery has similar capacity to the 24MX, but a slightly smaller footprint. It also has comparatively low cranking amps, suggesting that it also is pretty robust.
Motive SCS225: 130 amp hours, CA = 820A (from Trojan)
7"x14" footprint
This battery has greater capacity, and higher cranking amps. I assume the plates are of a similar design, and the higher cranking amps is a consequence of larger plates, not thinner plates. However, its footprint is getting up there if space is an issue.
Motive J185H-AC: 225 amp hours, CA not listed
7"x15" footprint
This seems like a nice choice, if you have space. I would probably choose this over two T105's. It's cheaper, smaller footprint, but it is taller.
30XHS-WNT: 130 amp hours, $220 USD. CA = 820A (batteriesinaflash, no spec from Trojan site)
7"x14" footprint
This seems very similar to the SCS225.
The charge cycle rating (number of discharge to 50% cycles) was only given for one line of batteries. It seemed to be around 1200 for higher capacity Solar Signature line, but the 12V batteries do have the 7"x14" footprint. I have no idea if that spec is similar for their other lines of high capacity deep cycle batteries.
You cannot change electrochemistry. It is what it is. If you want 12V, you need lead and sulphuric acid. Period. The difference between batteries will be the design of the plates, and the medium for the electrolyte. Batteries that need good cranking amps need lots of surface area on the plates because that is the only way to get lots of electrons out of the battery fast (that's current, in amps). This can be achieved by using thin plates or spongy lead. This seems to reduce the life of the battery if discharged too deeply, so deep cycle batteries need stronger plates. The way to get stronger plates is to make them thicker which reduces the surface area, reducing the cranking amps. The reason I was so confused about deep cycle, marine, and auto batteries is because there is a continuous spectrum of batteries from deep cycle to auto. Some batteries that are classified as deep cycle actually can produce enough current to start a motor. If they are decent batteries, they are usually larger, so that is why the can be classified as marine/deep cycle. They should have a decent charge/discharge cycle.
If I were to hypothesize as to which battery is best for a trailer, I'd side the one that has low cranking amps and high capacity. A small sized battery with lots of capacity is not going to give you many years of service. High cranking amps is not better for trailers, in fact it's worse. If you can find one that has no cranking amps specified, that's even better.
One last thing. If your battery is not accessible when closed, it will be very difficult to maintain through the winter. I thought about using a battery protector, BUT there is a discharge rate even when not connected that can range anywhere from 2-15% per month. So, your battery protector might open the connection when your battery gets down to 12V (50%), but my spring time it may have dropped another 30-40%. Given this, nothing replaces being disciplined and removing the battery and putting it on a trickle charger once per month. I was about to go an order a protector, but now that I think of it, it would be a waste of money. So, take that battery out and trickle charge it a few times over the winter.
deep cycle battery choices
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