Adding extra batteries

[AnneBinMaine]

We boondock a lot and are investigating rooftop solar. Part of doing that would be to add two more batteries. Has anyone done so with battery add and where did you put them. The most logical place would be in the storage compartment to the left of the entry door. The floor of that compartment looks like it might not be strong enough. Suggestions?

[TitanMike]

When adding batteries the "where" will depend on the type of battery.

If a regular lead/acid deep cycle battery, 12 volt marine deep cycle or 2 6 volt golf cart batteries in series, outside ventilation will be required.

If AGM type battery, they vent very little hydrogen so ventilation is less an issue although some should be provided.

If Lithium (LiFePo), they can be installed anywhere like at the bottom of a closet or under a bed.

Another thought if you want to check several boxes at a time is to step up to the plate and install two LiFePo batteries, replacing the existing batteries.

This would:

Double the usable power in the same footprint. LiFePo batteries can be discharged fully without the 50% discharge limit required for Lead Acid in order to get some reasonable life out of them. No need to install batteries anywhere else.

Cut the weight of your battery bank. On average each battery, a single 12V 100 amp hour or one 6 volt 225 amp hour battery will average around 65 pounds. Add two more batteries to your existing batteries and you'll have around 260# of batteries. Install two LiFePo 100 amp hour batteries and you'll have the same available power (amp hours) as four batteries (if you don't discharge below 50% to maintain battery life) and they will only weigh 66# in total.

LiFePo batteries charge faster. Mine charge at close to 50 amp and depending on how deep I've discharged them it takes from two to four hours max to fill them to the brim. Lead acid batteries of the same size and depth of discharge will take 8-10 hours or more to fully recharge. If charging from a generator that's a lot of fuel (and noise).

Last part, most LiFePo batteries have a long life, up to 5,000 cycles. Chances are great that anyone over the age of 50 will never need to buy batteries again to provide power to their RV. Only starting batteries if a motor home as the Lithium batteries don't provide the high starting current required.

Yes, there is more expensive initial cost. My Battleborns cost me $800 each but as the saying goes "One and done".

Another saying "It's not how much you pay, it's how often you pay it." Depending on how one uses their RV house batteries, and the type of batteries, average replacement time is between 3 and 5 years. Fully discharge a LiFePo battery and recharge it every day and it should last a minimum of 8 years Use them for 5 days and recharge, week after week, year after year, and you should get a minimum of 40 years.

(based on mfr's claims of 2,000-5,000 cycles)

[AnneBinMaine]

Thanks TitanMike for a very interesting reply. Don't think the Battleborns are in the budget at the moment. I printed out your info and will keep it in my RV folder.

[lcv800]

So Mike, how do they work if they are on a solar charger that continually charges daily (assuming it's sunny)? Would it be 365 charges or roughly a lifespan of 15 years?
Rusty

[TitanMike]

Originally Posted by lcv800

So Mike, how do they work if they are on a solar charger that continually charges daily (assuming it's sunny)? Would it be 365 charges or roughly a lifespan of 15 years?
Rusty

If the battery is fully charged and the solar controller is merely on "Float", that doesn't count as a "Cycle". A cycle is when the battery is discharged and then fully charged.

FWIW, the LiFePo batteries I see commonly offered as "drop in's" for RV house batteries will go to zero charge current when fully charged, controlled by the internal BMS.

Some Solar Controllers also shut off charge after a specified period of time, depending on how you program.

It's recommended by Battleborn that charging be shut off when fully charged and only recharged when state of charge has been significantly reduced. I just ordered a $9 "Module for my PD9160L Converter that will allow my Victron Battery Monitor to turn the charger off when it reaches a set state of charge and turn it back on when SOC drops to whatever I program into the Victron monitor. This uses the relay that's part of the monitor.

My "parasitic" loads are less than 1 amp and I have 200 amp total capacity. If I shut down the converter at 80% or so, let the batteries just sit until they reach 50% SOC, the charger will kick on and bring back to 80% approximately once per week.

I could just go turn off the battery switch and let batteries sit with TT powered up by converter but I'd rather automate. The relay is there in the Victron and for $9 it's the kind of project I kind of enjoy. Hardest part will be running a pair of small wires from Converter to Victron and then just programming for On/Off settings. Also plan on adding a switch to the control wires so I can override the Victron relay. With the module, when control wires connected to each other it turns the Converter Off and when "open", the Converter is off. Progressive Dynamics started offering this feature at the request of "Smart" LiFePo batteries.

For those unfamiliar with LiFePo batteries, according to what I've found in research they last longer when kept between 50% and 80% state of charge when not being used. They do not "like" float charging as again, according to what I researched, the Li-Ions are then converted to Lithium which reduces capacity over time. The lithium is plated on internal elements by the constant charge.

[TitanMike]

Originally Posted by AnneBinMaine

Thanks TitanMike for a very interesting reply. Don't think the Battleborns are in the budget at the moment. I printed out your info and will keep it in my RV folder.

You are welcome.

I am just sharing what I've learned for the benefit of those who may be on the fence. Yes, they are pricey and not everyone has the budget for them. Flooded Lead Acid batteries remain the lowest cost per amp hour capacity but also have the heaviest "footprint" along with more "babysitting" requirements.

The reason I went to the LiFePo batteries was two-fold. One was to get weight off the tongue of my trailer and second, move the batteries into a warm compartment so freezing weather wouldn't reduce the capacity. To me it was worth the price and thanks to my late wife's frugality, "they were in the budget".