battery selection

[Dominator]

To all the guru's out there. i am looking to upgrade my second battery. At the moment i just have a marine battery for my second and i want to get something to help the fridge last longer. The problem i have is that my amp for my stereo also runs off the second battery and at peak it can draw up to 60 amps. So if i get a deep cycle battery will the amp damage it because of its high current draw? Even if the amp is only drawing high current when the car is running? What about AGM batterys or one of the alround (deep cycle and starting) batterys. Any info or help would be greatly appreciated. FYI it is on a deisel patrol with a 120amp alternator.

[DamTriton]

Probably better off with a marine type battery due to tha amp if you are using a wet cell "sloppie".

Other option would be an AGM like an Odyssey which are pretty good at both, good energy density (AH per kg, AH per cm3) or you could try an Optima but the energy density isn't as good due to air spaces caused by the cylindrical cells per height/width/depth (still way better than a sloppie).

[drivesafe]

Hi Dominator, the blunt reality is that your stereo should only be used while your motor is running.

Even at half that amperage, you are going to kill batteries in a very short time.

Most batteries should be loaded with a constant current draw of more than 10% of the battery’s total capacity.

Short periods of high current draws are not a great problem but your probably planning on running your sound system for long periods of time.

The problem with pulling high currents from a battery is that the higher the current draw, the less power the battery will supply.

Different types of batteries act in slightly different ways but basically what this means is that if you draw a 1 amp load from a 100 Ah battery you should theoretically get 100 hours of use.

Draw a 5 amps and you might get 20 hours of use, draw 10 and you will be lucky to get 7 hours, and in your case a 60 amps load would both flatten and stuff the battery in about 10 to 15 minutes.

The only other alternative ( as noise is obviously not a problem ) would be a decent sized generator.

[Dominator]

I nearly always only use the stereo while the car is running. If i have the stereo on with out the car running i turn that amp off so it is not drawing a large amount of current. I am also considering installing a capacitor to even out the current draw so it is not so much high current pulse and more a meidum current constant. I think I will get my self a agm battery.

[drivesafe]

Hi again Dominator, if you go for an AGM, as DAMKIA posted, the ONLY batteries that could tolerate that sort of current draw or anything near it, on a constant rate is a SPIRAL WOUND AGM like an Odyssey, an Optima or and Exide Orbital.

You CAN NOT use a flat plat AGM, like Fullriver and similar, for anything more than standard low currents.

[Dominator]

Cool. thanks for your help.

[DamTriton]

Hi again Dominator, if you go for an AGM, as DAMKIA posted, the ONLY batteries that could tolerate that sort of current draw or anything near it, on a constant rate is a SPIRAL WOUND AGM like an Odyssey, an Optima or and Exide Orbital.

You CAN NOT use a flat plat AGM, like Fullriver and similar, for anything more than standard low currents.

Minor correction to this - the Odyssey is a flat plate AGM and is suitable for high current use.

Also note that farad capacitors will onle "take the edge off" the current spikes and will still allow the battery to be damaged if the max current is drawn. Don't believe "ricer tech". At (say) 50 amps the capacitor will only cover a few milliseconds of surge current.

[Dominator]

if i was to run my amp off my start battery and just the fridge etc off the second battery could i go to a normal deep cycle battery or is the current draw still going to be a problem?

[drivesafe]

Hi again Dominator, short of fitting 4 or more batteries ( not a realistic idea ) there is no way to run any high current device for long periods of time, thats anything longer than a few minutes, without doing serious damage to any battery, cranking or deep cycle.

You could get some operating time from something like an Optima but it would still be limited to, if your lucky, 30 odd minutes from a 100 Ah Optima type battery.

I wasn’t joking when I suggested getting a generator. This is the only way you could run what you are trying to do.

Look, just to give you an idea of whats needed to run even medium current consuming devices. These mobile Coffee shops need 8 or more 100+ Ah batteries to maintain 30+ amp espresso machines and there not standard automotive batteries, yet their batteries still have short operating life spans.

[poppywhite]

Hi again Dominator, if you go for an AGM, as DAMKIA posted, the ONLY batteries that could tolerate that sort of current draw or anything near it, on a constant rate is a SPIRAL WOUND AGM like an Odyssey, an Optima or and Exide Orbital.

You CAN NOT use a flat plat AGM, like Fullriver and similar, for anything more than standard low currents.

Hi drivesafe,

This is first I've heard this about spiral and flat pac batterys, Can you give or point to some more info on this please? In past I lived on battery and panel, and friends, with more rescources live on independant off grid power,
Some use the huge 1100 AH 2v cells in 12 or 24v configeration, thesr are flat pack, and some dont seeem to have long life others use trogen or similar traction batery. We all believe it is refigeration that kills them "prematurely"

I have always thought spiral optoma v flat pac deep cycle type was more marketing.

As for op question 60A is very large draw! I think a inverter ~~style generator is only way to do this. and have power to spare.

[tehekho]

Given that you'll switch your amp off when the car isn't running, you'll have no worries.

The 60A (I'm assuming around 600w) current draw you speak off is only going to be transient anyway. Don't waste your time with a capacitor. I had one on my stereo which would blow 200A Fuses on a good burp and it made SFA difference - it's just rice bling

[drivesafe]

Hi again Dominator, if you go for an AGM, as DAMKIA posted, the ONLY batteries that could tolerate that sort of current draw or anything near it, on a constant rate is a SPIRAL WOUND AGM like an Odyssey, an Optima or and Exide Orbital.

You CAN NOT use a flat plat AGM, like Fullriver and similar, for anything more than standard low currents.

Hi drivesafe,

This is first I've heard this about spiral and flat pac batterys, Can you give or point to some more info on this please? In past I lived on battery and panel, and friends, with more rescources live on independant off grid power,
Some use the huge 1100 AH 2v cells in 12 or 24v configeration, thesr are flat pack, and some dont seeem to have long life others use trogen or similar traction batery. We all believe it is refigeration that kills them "prematurely"

I have always thought spiral optoma v flat pac deep cycle type was more marketing.

As for op question 60A is very large draw! I think a inverter ~~style generator is only way to do this. and have power to spare.

Hi Poppywhite, it’s one of the many confusing issues surrounding the different types of batteries.

With AGMs there are two basic types, your automotive grade, like optima, Odyssey and Orbital which are all specifically designed to be direct replacements for conventional flooded wet cell cranking batteries.

Then there are the NON automotive grade AGMs, like Fullriver, and this type of low grade AGM makes up the bulk of the AGMs used in the RV industry.

The quickest way to pick if an AGM is a true Automotive grade AGM is to get the battery’s specs from the manufacturer’s web site.

If the battery has a maximum charge voltage of 14.4v then it is NOT an automotive grade AGM.

Genuine automotive grade AGMs will have maximum charging voltages similar to or higher than standard wet cell cranking batteries, 14.7v or greater.

Most AGMs in automotive and RV use are actually batteries made for RAPS ( Remote Area Power Supplies ) and UPS ( Uninterruptible Power Supplies ) like for the telecommunications industry.

These low grade AGMs can be used quite successfully in RV situations, but you must allow for the short falls.

Low grade AGMs do not tolerate high vibration situations, and as pointed out above, must not be charged with voltages above 14.4v and something most people are not aware, standard AGMs are CHARGE CURRENT LIMITED, again check the manufacturer’s web site for the exact specs for what ever AGM battery you have.

AGMs like Fullriver, have a maximum tolerable CHARGE and DISCHARGE current of 20 to 30% of their total Ah capacity.

Depending on which Fullriver battery you have, they will have either a 20% or 25% maximum charge current and some other brands of standard type AGMs will tolerate as high as 30%.

Whereas genuine automotive grade AGMs will tolerate full inrush currents. In other words, they will literally take everything you can provide.

[Dominator]

yeah i am not going to worry about the cap. was not sure how usefull it would be any way. I think i will just go for a marine 110amp battery and not use the amp while the car is turned off.

[DamTriton]

One other common mistake is to confuse AGM with gel type batteries both come in plastic cases with no fill caps. Gel batteries are definitely in the low current only arena.

Easiest way to check whether you have a deep cycle AGM pr an automotive type is to check for the maximum inrush current allowable. Automotive AGM's have no maximum charge rate only a maximum voltage they can be taken to under charge, whereas the deep cycle AGM's will be primarily current limited.