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Old 05-09-2007, 03:42 PM   #1
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Good question, I was wondering the same thing. Friend of mine pointed me in the direction of Optima batteries as being the best deep cycles out there.

I think I am going to have a battery selector switch and switch between running off of the alternator while on the road versus running off the deep cycle only when I am not running and not near a power hook up. When at a camp-ground will have an AC power hook up.

Then I will only plan on charging the deep cycle when I am near AC power hookup. Though I will not be running off of the deep cycle unless I absolutely have to.

Another question I have is how do you determine how much battery capacity you need compared to your power draw. I am setting up a 3000/6000 Watt inverter but only plan to run the fridge and microwave off of the batteries if we are not near power hookup.
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Old 05-09-2007, 06:00 PM   #2
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We've had discussions about this topic a few times before on the board. The general consensus is that the alternator is not the best method of charging the batteries, but aside from solar, is the only method available. It's not that an alternator doesn't do a good job of charging batteries. In fact, it's about one of the simplest methods out there and works rather well. The problem comes from the fact that it is voltage sensing and will taper the charge off as the battery approaches a full charge. The end result is a deep cycle that will sit somewhere between 90-100% charged after a reasonable amount of driving time. For most purposes this is fine. It just means that you can't count on the alternator to be your only means of charging the batteries.

I would recommend getting an intelligent onboard converter/inverter/charger, a good portable automatic charger, or get a manual charger and be prepared to be a little more hands on. Schumacher makes a good automatic charger called the Speed Charge that has 2-8-12 amperage settings and a setting for AGM, Deep Cycle, and Starting battery algorithms for charging. We sell them here for $75. Your mileage may vary. Deltran also makes some of the very best automatic chargers on the market and would be worth looking in to. Basically you're just going to want a charger to bring the battery up to 100% charge, desuphate, and equalize the battery as required.

As for batteries...I would keep away from the Optimas or clones. I sell them on a daily basis and see absolutely NOTHING wrong with them...when used in the correct application. Unfortunately and RV is not the correct application. A Group 31 Optima Marine Deep Cycle (blue top) only has 75 amp hours in it. A pair of them is going to give you 150 total amp hours to a 100% depth of discharge for $450.

A GC2 6 volt golf cart battery will give you about 200 amp hours, give or take and cost $75. You will need a pair of them to get to 12 volts obviously, but you will end up a far greater capacity (meaning a shallower depth of discharge and longer living batteries) for 1/3 the price in about the same footprint.

An alternative to the wet acid golf cart batteries is a standard flat plate AGM battery. It uses the same technology as an Optima, but the plates are flat so you fit more in a given volume of battery. We currently are selling one as a middle of the road option to people with boats in a Group 27 footprint that has a capactiy of 100 amp hours (the same as a wet acid Group 27 and 33% better than a Group 31 Optima) for $170. This is CERTAINLY not the only option as far as AGM's go, but can perhaps serve as a starting point for comparison.

Basically what it boils down to is deciding your electrical load needs versus maintenance versus cost, etc. Dollar for dollar wet acid golf cart batteries are still the way to go for the vast majority of us. The closer you get to boondocking full time the more sense AGMs start to make. If you are just looking for a back up power source when shore power is not available, but plan to spend most of your time in campgrounds then the wet cells probably make the most sense.

I'm sure some others will pipe in with some advice, but in the meantime I would recommend reading Phred's Poop Sheets
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Old 05-10-2007, 02:28 PM   #3
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A product of any discharging, be it intended or unintended, of a battery is that suphation will form on the plates. This is no big deal when you recharge the batteries right away because it is converted back into lead. If they are constantly resting at 90% charge that suphation will turn rock hard and that area of the plate in a cell will essentially become "dead." Eventually you will then be working with 90% of the original 90% and so on. You will lose capacity, but it will take time.

The alternator will not overcharge the batteries so long as your regulator is doing its job and you aren't pounding a 200 ah battery bank with some astronomical amount of amps at any given time. The general rule is to aim for about 25%. That means you should aim for about 50 amps max at any given time which should be right in line with what your alternator will ACTUALLY be putting to the batteries, not its rated output. A high dollar adjustable regulator can be piece of mind for you.

The biggest advantage to having a good external charging method of some type is that you will top the batteries all the way off keeping them from getting "lazy" at a voltage or suphating. It will also allow you to occasionally equalize the stratified acid.

As for the practical side of things, yes I have seen all this to be true. It's absolutely amazing what you learn when you have a pile of batteries of your own and start taking care of them because you learned how to take care of them (through work in my case). There are a ton of battery myths out there and it gets rather confusing. NiCd batteries are best stored discharged and should be fully cycled every 3-5 cycles. NiMh doesn't have as much of a memory effect and can sit at a partially charged state better, but has its own set of rules governing charging and usage. Lithium Ion has some very specific properties pertaining to cutoff voltage and how the cells actually will grow in capacity over their lifespan before tapering off. Alkalines CAN be thrown in the garbage. You don't have to bring them to me mixed with a bunch of other battery types for recycling only to have me sort them out and put them in the garbage. That brings us to lead acid. Lead acid is one of the most forgiving battery chemistries out there. The only thing you really need to remember is that they like to be worked. Up and down, up and down. They like that.

If you're really looking to keep those batteries alive longer the best hting you can do is charge them in the off season. Most people will pull their batteries out of a rig and put them in the basement to sit from October to April or May thinking that is all they need to do. Unfortunately wet acid batteries tend to lose about 3-5% of their charge per week while AGM's will do about the same in a month of just sitting. It's not much, but after 3-4 months go by your batteries are goners. For some people that's ok given the price versus hassle debate. For others charing them every 4-6 weeks as recommended is easy enough. Still others refuse to do the offseason maintenance and then like to come into the store and try to get a frozen battery warranted (charged batteries won't freeze for all intents and purposes).

What it all boils down to is finding something that works for you in your situation. If you don't mind shelling out $150 every two years then minimal maintenance is required. If you want your batteries to be the best until the end or last 5 years a little more maintenance is required. If nothing else, I would consider getting a Deltran Battery Tender or similar atleast for storage. If it makes your batteries last twice as long it has paid for itself three times over.
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