Take extra batteries when boondocking?

[okmunky]

I boondock 7-8 months per year and I have 272 watts of solar panels glued to the roof of my class C. They are Unisolar monocrytaline type panels -- only 1/4 inch thick and they have served me well and charged my 2 golf cart batteries (just bought 2nd set -- $85@ at Costco) for over 5 years. So now you know my point of reference.

Have you compared the cost of the portable folding solar panels to the cost of the Trojans? How about the weight? I hate running my generator even tho it's not noisy by generator standards. And there were over 50 portable generators stolen in the Quartzite LTVAs alone this winter.

At 62 pounds each muscling T-105s around will make an old man out of you fast. Portable solar can easily be moved to your next RV.

[EV2]

Keep in mind that some locations like Organ Pipe severely limit the hours that you are permitted to run a generator.

[rarebear.nm]

Plenty of good info here, but one thing I think was missed, When you have a set mismatched batteries, by age, capacity (AHr), etc. the weaker one(s) will become parasitic on the good ones and run the entire system down. If you have the same make/model but different aged batteries as their life becomes shorter the amp hour capacity becomes that of the weakest single battery. These set ups are not simply additive.

When wiring up four or more six volt batteries in series/parallel it also makes a difference in recharge cycle aging as to how the connections are made. You want to connect the hot and ground wires to the two opposite 2-six volt pairs, not both connects to one pair.



Connecting both leads to the top pair will work, but you'll be pulling more power from that pair and not equally from the entire battery bank.

Recharging batteries with significantly different (say 100 vs. 240 AHr) will end up over charging the lower capacity battery and likely damaging it quickly, perhaps with much spark and smoke or worse.

Have fun and be safe.

[twinboat]

Originally Posted by rarebear.nm

Plenty of good info here, but one thing I think was missed, When you have a set mismatched batteries, by age, capacity (AHr), etc. the weaker one(s) will become parasitic on the good ones and run the entire system down. If you have the same make/model but different aged batteries as their life becomes shorter the amp hour capacity becomes that of the weakest single battery. These set ups are not simply additive.

When wiring up four or more six volt batteries in series/parallel it also makes a difference in recharge cycle aging as to how the connections are made. You want to connect the hot and ground wires to the two opposite 2-six volt pairs, not both connects to one pair.

Attachment 154143

Connecting both leads to the top pair will work, but you'll be pulling more power from that pair and not equally from the entire battery bank.

Recharging batteries with significantly different (say 100 vs. 240 AHr) will end up over charging the lower capacity battery and likely damaging it quickly, perhaps with much spark and smoke or worse.

Have fun and be safe.

There are a few sites that don't support that mixing different AH capacity is a problem.

Here is a site with an explanation.

https://www.homepower.com/articles/s...eries-parallel

Connecting two banks with different capacities in parallel is technically fine since the batteries will be operating at the same voltage. Charge and*discharge current will be shared, based on capacity. It is best if the batteries are of the same type and age. For example, avoid combining a sealed*(gel or absorbed glass mat) battery with a flooded (conventional) battery because they have different charging setpoints. Broadly speaking, you can*parallel batteries without problems, and the charge controller will look after them. Just make sure you give them plenty of charge. If the system*tends to operate at less than a full state of charge, adding new batteries to old will probably just result in the old ones pulling the new ones down*and everything getting sulphated.

[Dooger54]

And here I thought this thread was done last week! Lots of great info here for anyone dry camping though. Answers to a few things posted recently-

I do not plan on using mismatched batteries so that isn't an issue for me. I would only use two at a time and those two are same type and age.

I have looked at the portable RV solar systems made by Zamp and Go Power. I like the portability, I have no desire to mount units permanently on my roof. I see two problems - 1). Expense. For a 160-180 watt system you are looking at about $750. This does include the controller and cables. 2). These systems mount the controller on the solar panel. In most cases this will be around 15 feet from the batteries. My understanding is to get the most efficiency the controller needs to be no more than maybe 6 feet from the batteries.

Lot of good comments on people using generators. I still shy away from that, I just don't see the need right now and would rather not use one. Just my personal feelings. I don't use much AC power when dry camping, I don't even have an inverter. And I don't plan on dry camping more than 4-5 days at a time, usually only 2-3. We like to move around a lot and usually don't stay in one place more than 4-5 days max.

[nothermark]

Originally Posted by rarebear.nm

Plenty of good info here, but one thing I think was missed, When you have a set mismatched batteries, by age, capacity (AHr), etc. the weaker one(s) will become parasitic on the good ones and run the entire system down. If you have the same make/model but different aged batteries as their life becomes shorter the amp hour capacity becomes that of the weakest single battery. These set ups are not simply additive.

When wiring up four or more six volt batteries in series/parallel it also makes a difference in recharge cycle aging as to how the connections are made. You want to connect the hot and ground wires to the two opposite 2-six volt pairs, not both connects to one pair.

Attachment 154143

Connecting both leads to the top pair will work, but you'll be pulling more power from that pair and not equally from the entire battery bank.

Recharging batteries with significantly different (say 100 vs. 240 AHr) will end up over charging the lower capacity battery and likely damaging it quickly, perhaps with much spark and smoke or worse.

Have fun and be safe.

Wrong in so many ways. As long as the batteries are in parallel the load share will tend to share according to the internal resistance of the batteries. That increases with age so the older batteries will do less. The charging current will apportion the same way so one set will not overcharge while the other is charging. About the only other thing that will change out how current is shared is the wire resistance.

The only reason not to mix batteries of the same type but different age is that the newer batteries will work harder thus die sooner. Sounds terrible but really is cheaper to add a new set knowing it will be the whole system when the new setup dies. Better than tossing the partially used set just to have all new.

A lot of that goes out the window if you mix chemistries.

[wingnut60]

Ran all last summer, inc trip to AK, with 2 4-yr-old T105s as main batts, and 2 new 12volt SLAs from Sams. All were wired together and charged by the 80amp converter. Had no problems with this arrangement.

[okmunky]

I would think you could get by with a 100 watt solar system. Here's one with good ratings for $199.

https://www.amazon.com/ECO-WORTHY-Po...solar+portable

Putting it within 6' of your batteries is only a matter of parking in the right direction. But I'm a solar fan so that's what I know and it works for me.

[rarebear.nm]

We are all entitled to our opinions, my prior posting is in part based on information provided by Trojan Battery on their website an dothers:
Frequently Asked Questions | Trojan Battery Company

On the second screen page it reads:

11. Can I do a partial replacement of my flooded batteries?
We do not recommend partial battery replacement of flooded battery banks. The behavior of batteries during discharging and charging varies throughout their lifespan and if all the batteries are the same age, than they all will have similar responses. The danger with replacing only one battery is that the older batteries tend to require more charge than newer batteries, and since the new batteries are in the same circuit, they too will be overcharged. There is also the chance that the older batteries will be undercharged since the overall voltage response of all the batteries (old and new) will not be a good representation of either group. The charging system might erroneously think that ALL the batteries have reached the desired voltage and it may stop the charging of the batteries prematurely.

I know many people have mixed different aged batteries, including myself and experienced no noted bad results. Unless you have better researched sources, I'll stick with my prior posting.

Another post at:
Why should not batteries of different age be connected in parallel? — northernarizona-windandsun


Re: Why should not batteries of different age be connected in parallel?

Batteries change their parameters with age/cycling/temperature/brand/model (talking here about lead acid batteries).

More or less, you get optimum performance with matched cells. This is done quite a bit with RC Models and such.

Say you have two batteries in series. If their capacity is different (unmatched due to age/cycling/condition/or even different brand/models) and you want to avoid discharging below 50% (for long life) and below 20% State of Charge (to prevent a cell from becoming reversed biased and instant cell/battery death)--You are limited to the capacity of the weakest member of the series string. So placing a "new" and "old" battery in series--It will (usually) be the old battery that limits capacity (and will probably eventually fail first).

Another issue is that old batteries have higher "self discharge" than new. When you have two batteries in series, again old vs new, the old battery will self discharge faster and become "out of balance" with the new battery. The usual method to equalize a battery bank is to "over charge" the good battery (force excess current through the good cells to get charging current into the low cells). Equalization is hard (in general) on lead acid batteries. It erodes the plates, uses water (or catalyst in AGM/Sealed batteries) and causes positive grid corrosion (oxygen forms on the positive plates during equalization). And an out of balance battery bank--The low state of charge cells will again limit the series string capacity. And equalization will cause the newer battery to age faster (equalization also increases battery temperature. 10C increase in battery temperature, 2x faster aging).

There are also problems with cells/batteries in parallel. The idea is to design your wiring such that you have equal current flow during charging/discharging. Older batteries have higher internal resistance (less charging/discharging current due to plate sulfation) and as they sulfate, lowering operating voltage (accept more charging current, supply less discharging current as battery voltage is proportional to specific gravity... Lower SG, lower battery voltage).

And since during charging, low battery may gas more (less capacity, charges "quicker", lower SG and more gassing as more sulfur is locked into lead sulfate), old batteries can heat faster than the parallel new batteries. Higher temperature, lower charging voltage, accepts more current, lower charging current--repeat)--And you can have thermal runaway issues with your parallel bank. While the new batteries get cycled deeper and get less charging.

Another issue is that you need to monitor cell/batteries in a battery bank for consistent operational voltages on each cell/battery (charging, discharging, resting), specific gravity, and use a DC Current Clamp meter to ensure that parallel strings are properly sharing current between strings. An open cell will kill the current in a string, and a shorted cell will "over charge" the other cells in the string--And discharge the other parallel strings.

So--if you have a "mix" of unmatched cells/batteries in your bank--You will have to keep a very close eye on them as you will be running "more often" with some sort of aging/failing cells (i.e., 2/4/6 year old mix of batteries--You will have a battery/cell failure every ~2 years if you assume a 6-8 year battery life). So, a mixed bank of batteries with a good chance of cell failure every 2 years to catch/diagnose/replace vs a, hopefully, uneventful 6-8 year battery bank life--And replace all batteries at the same time (when one or two start to go, there will be others not too far behind).

Not to say that people do not mix old and new batteries. There are a few people here that have large Forklift batteries. Say a 36 volt battery that they only need 24 volts from... They get a used battery, test each cell, and find 12 good cells out of the 18 in the battery bank--Rewire for 12 good cells (matching) and then get many years of extra life out of the "junk" battery. May even have a few "spare" cells that can be wired in when one cell does die.

So--Mixing old and new cells/batteries together is not (usually) going to give you a pile of melted plastic and lead, with battery acid flowing down your floors in two weeks... It is more of an issue of overall battery bank reliability and how much is your time worth to keep a mixed bank operating (and close monitoring to avoid catastrophic failures--Which can happen at anytime with old or new batteries).

There are many similar articles on the web from places I'd consider to have some authority on this issue.

[nothermark]

So adding a second set of same chemistry will probably give less than perfect results. OTOH few folks are worrying about winning a race or maximizing results. It's a lot easier and cheaper just to put in enough overkill to handle the load then optimize a bit when replacing everything down the road.

[twinboat]

I agree with Trojan on the statement you published.

" 11. Can I do a partial replacement of my flooded batteries?
We do not recommend partial battery replacement of flooded battery banks. The behavior of batteries during discharging and charging varies throughout their lifespan and if all the batteries are the same age, than they all will have similar responses. The danger with replacing only one battery is that the older batteries tend to require more charge than newer batteries, and since the new batteries are in the same circuit, they too will be overcharged. "

But we're not talking about replacement, we're talking about adding capacity to a good, funtioning battery bank.

We can all go back and forth with websites, fore and against adding new to old batteries, but the point is it is not going to kill your new ones doing it.