Thread: Deep cycle batteries

As mentioned deep cycle batteries are usually only recommended to be discharged to 50% of their capacity. If you continue to go past 50% then you will dramatically reduce thye life of the battery

The way I see it, the real advantages of AGM batteries is the ability to be completely discharge the battery a number of times without severe long term effects, the ability to mount them inside a vehicle/caravan and the ability to use as acrank battery if needed. I have used Optima batteries for a few years now without any problems, other then the price. I would consider the new range of Full river batteries from China if price is a major consideration.

No matter what battery you are buying, one must think about what its really being used for, ie: do I really need one that big? Can I charge one up when its flat with what Ive got ? Is the charger that I have suitable?
Calcium batteries need a special charger, same as Gel/Agm. Voltage and temp is critical when charging a sealed battery. Too much voltage/amps will make your battery gas and heat up and it wont vent fast enough resulting in the battery swelling up and drying out. Calcium batteries when near the end of a charge cycle have low resistance thus equals high voltage and a normal three stage or automatic charger see this as fully charged and turn off, which is wrong. The battery has tricked the charger into thinking its charged. With the correct charger this will not happen. In response to a question posted earlier about changing a 12v-7 amp battery for a glass matt type, the correct 12v-7 amp installed in the fail safe system is a SLA "sealed lead acid glass matt battery" The acid is absorbed in the glass matting that is around the plates keeping them moist and the battery vents through tiny holes and rubber seals within the batteries lid. Thats why charge rates are critical, cut one open and see whats inside, its interesting. Where I work we forever see people buy batteries that are too big for their charging system and the battery is continually run flat and they complain about how it wont go as long as it did when they first got it ( so it has to be faulty of course), so in their wisdom they go and buy another battery to put alongside their first one so now they have heaps of AMPS, but still dont change the charging system and now have 2 flat batteries that are slowly sulphating and dying and when they do die at an early age it has to be the batteries fault and nothing else can be at fault. Sorry about all that , but thats my whinge for the night, its 12.35 am and its time for bed. Remember dont buy a battery because it sounded good in a book/magazine. Its supposed to !!!
Oh and one last thing, it is easy to check if a battery is fully charged ... use a hydrometer ! or use a voltmeter. A fully charged battery that has been let sit for 24 hrs after being charged should read at least 12.6 volts. Each cell in a battery generates 1.1 volts when charged to a specific gravity of 1260. 1260sg is the rating of acid used in batteries designed for use here in Aust. byeeeeeeee

Hi zwitter, I must post a warning for anybody considering your 240 volt set up.

There is nothing more dangerous than running around in a vehicle with an inverter cranking out 240 volts AC.

If your vehicle is involved in an accident, there is NO 100% WAY TO GUARANTY THE AC IS SAFELY SHUT DOWN and as such, there is no warning that a vehicle may now be electrified and potentially fatal to not only you but to anybody who may come to your assistance.

The use of inverters while driving, has been debated on a number of other sites, not only is there no way to make this type of set up 100% fail safe, it is questionable as to whether there is any real advantage to using such a set up and even if there is an advantage, the amount of advantage is so miniscule that the set up is just not necessary in the first place.

Next, in the case of auxiliary battery use, not discharging them below 50% SoC is only a yard stick to try to work to but if you use the graphs that some battery manufacturers supply showing the rate of discharge levels verses the expected effect on the life span of the given battery, you will find that in most cases, you can take the battery down bellow the 50% and the battery’s life span will not shorten any less that the battery’s normal expected life span when used in ideal circumstances.

To put it in a more understandable way and I might add, a very simplified explanation. If, according to a given manufacturer, their battery can only be discharged down to 25% SoC 50 times before the battery’s sustainable capacity is likely to be below 80%, ( or the battery will no long be able to hold more than 80% of it’s original stored capacity ) then taking your camper trailer out once a month and discharging the battery down to 25% every time you take the C/T, out would mean you can only expect to get a little over four years operational use out of the battery.

Now if this same battery has a normal expected life span, when used in ideal circumstances, of four years, theoretically, your not going to get any better life span if you don’t take the below 50%.

There is a host of other things that have to be taken into consideration, that will have an effect on the battery’s life span besides just how low you discharge it. Another important consideration is how soon you start to re-charge the battery after it has been discharged. The longer you leave the battery in a discharged state, the quicker the battery is going to fail to be able to be fully charged.

Cheers.

Originally Posted by bellaposs

Oh and one last thing, it is easy to check if a battery is fully charged ... use a hydrometer ! or use a voltmeter. A fully charged battery that has been let sit for 24 hrs after being charged should read at least 12.6 volts. Each cell in a battery generates 1.1 volts when charged to a specific gravity of 1260. 1260sg is the rating of acid used in batteries designed for use here in Aust. byeeeeeeee

Hi bellaposs, hydrometers, obviously, can a only be used with wet cell batteries but even so, when using the best quality hydrometer on wet cell batteries or the best quality volt meter to check the SoC of any type of battery, even when you leave the battery in a No Charge / No Load state for at least 72 hours, this type of measurement is still only be 95% accurate.

As I posted, there is no effective way to tell if a battery is 100% fully charged without carrying out laboratory testing.

There is an electronic hydrometer in the states that is immersed in the battery’s electrolyte for a few second and will then give a 100% accurate SoC reading, but the device costs around $2,000 US so not really a device I would expect to see being carried by your average weekend warrior and again, it is only useable with wet cell batteries.

Again, my argument against statements that a battery is or is not charged to 100% SoC, is based on the fact that this can not be easily proved and I always work on the basis, you can get a battery to 95% charged and that this is for all intent, a fully charged battery.

Cheers

MHO FWIW.
AGM/GEL batteries can be charged from a normal alternator, but should be set up with current limiting..

As I understand it excessive amps cooks the gel/warps the plates as the gel isnt as good at cooling as the acid in a flooded cell. as the nominal charging amps is at best only a handfull of tens of amps and the alternator will push out up to its limit (typically 85+) your running the risk of killing the battery even more than if you have just run it flat.

Or am I off the mark here?

Interesting thread this!

Dave, what you say is right, but an additional problem is the alternator. I doubt if the average 85 amp alternator would be very cheerful about pumping out its full output very often.

For this reason, I have deliberately used thinner than ideal wire from my alternator to my second battery, so that with a very flat second battery the max charge current is 30 amps. (Second battery 12 volts, alternator 14 volts, resistance in leads .067 ohms)

As the second battery assumes a full-ish charge, the current drops quite low, so that the loss in the leads is also low, and the battery gets virtually just as highly charged as it would with heavier wires. (Charge current 1 amp, alternator 14 volts, lead resistance .067 ohms, battery voltage 13.93 volts)

Heavy wires are essential between the second battery and the loads (fridge, winch etc) but not necessarily from the alternator.

I would prefer a proper 3 stage set-up, but this crude system will have to do. Good news Zwitter that something will be available eventually.

Good point drivesafe about the inverter hazard after a prang. Hadn't thought of that.

Cheers all,

Paul

Actually turning off the inverter after a prang should be quite easy to do...

get one of those impact sensors that is mounted on the bulkead of a TD5 defender (and others but I dont know where it is) wire that to a relay that provides the power to inverter...

From what Ive read from perusing manuals, these things are more sensitive than your airbag sensors.

Or you could just make sure that the prang wipes out the battery thats running the inverter but I think the first idea might be a bit easier to do IRL.

any reason why that shouldnt work?


Oh Ive just got off the phone with the old man... hes looking into desiging a stepped rate current limiter for me... this could be fun no more killed deep cycles for me and given its my old man you can expect it to do bloody everything for the battery from low voltage cut out, to correct charging from solar, mains or the alternator...

it'll probabley make coffee to.

Originally Posted by Merv

I have used Optima batteries for a few years now without any problems, other then the price. I would consider the new range of Full river batteries from China if price is a major consideration.

Are these a "Made in China" Optima/Orbital knock-off?.......what sort of prices[if they are]?????????