(2) 200ah vs (1) 400ah Battery

[NCW_Wander]

Are there any downsides to buying two 200ah batteries vs one 400ah battery?

While doing some pricing, I noticed on Amazon that I can get two 200ah LifePo4 batteries for $700/each ($1400+ total) or I can get one 400ah LifePo4 battery for $2k. Theoretically, wiring the batteries in parallel should get me double the wattage. And watts over time is the same as amps over time at the same nominal voltage… am I missing something? Is charging time slower? Does paralleling reduce battery life?

thanks!

[Guest]

That's a pretty amazing price for a 200ah battery. Only issue in buying a higher capacity battery than parallel connecting lower capacity batteries is if a failure occurs. Its cheaper to replace one 200ah battery than one 400ah battery. No losses from parallel connecting 2x200ah batteries as its treated as a single 400ah battery. Follow the manufactures recommendation on rate of charge where a typical charge rate to maximize longevity is 0.5C for a Lithium battery.

Jim

[Country Campers]

I agree that 2 is better than one, if one fails you still have one working. The only difference is that you have to wire the 2 together, make sure the wiring is large enough to handle what you are doing. Pros and cons each way.

Brian

[Cate&Rob]

When you connect the two batteries, use a high current marine four way switch. Batt 1 / Batt 2 / Both / Off. This makes it easy to choose what you want to include or disconnect. Remember that you will only be charging a connected battery . . . ask me how I know this last part .

Rob

[Guest]

NCW_Wander If these batteries are the "Ampere Time" units you may want to look these over carefully. First this vendor claims automotive grade cells which I seriously doubt. Auto grade cells have much higher density, typically are different chemistry and cost much more.

Some observations:

Their BMS has some limitations but with proper monitoring, this is not an issue.
Prizmatic cells are used in this battery where the potential issue with Prizmatic cells is that if one fails, the battery is shot. With cylindrical cells in a Series Parallel pack, a bad cell will just slightly lower the overall capacity of the battery but it will still be usable.
Cylindrical cells also reject heat more efficiently but this battery is CE certified, so.

The battery does come with a 5 year warranty and has an additional warranty offered by Amazon so there are pros and cons if this is the battery your referencing.

Jim

[howson]

Are there any downsides to buying two 200ah batteries vs one 400ah battery?

While doing some pricing, I noticed on Amazon that I can get two 200ah LifePo4 batteries for $700/each ($1400+ total) or I can get one 400ah LifePo4 battery for $2k. Theoretically, wiring the batteries in parallel should get me double the wattage. And watts over time is the same as amps over time at the same nominal voltage… am I missing something? Is charging time slower? Does paralleling reduce battery life?

thanks!

What is the maximum sustained amperage output of the 200aH battery vs the 400aH battery? The reason I ask is a standard 100aH Battle Born is capable of sustaining 100 amps. (I'm ignoring surge capability in this as it just gets too confusing.)

Why is this important? If you intend on matching the batteries with an inverter (like a Multiplus 3000VA) to get the full capability from the inverter the batteries must be able to provide 250 sustained amps of 12vDC (which is inverted to 25 amps of 120vAC). That's why to get the maximum possible capability from a Multiplus an owner must buy a minimum of three of Battle Born's 100Ah batteries.

Regarding the amps and watts question...not exactly sure what you're asking.

Forgive the soapbox, but if batteries were rated in watt hours instead of amp hours it would be much easier to compare batteries. For example, the voltage curve on a standard RV lead-acid battery is steeper then a Battle Born's. Using the first 50% of each battery, the Battle Born will provide more power (wattage) in the first 50 amps provided due to the higher voltage. If you're scratching your head...it's just math. I'd made the chart shown below awhile ago to "see" the difference. (For those who may not know, voltage times amperage equals watts, which is the measurement of work.)

Howard

[NCW_Wander]

howson , That's a good point to bring up. The capability of any electrical circuit is based on the actual voltage rather than the nominal voltage. As the voltage drops, more amps are required to perform the same amount of work. When voltage gets low on the power grid, I increase the VAR output of a generator, close a capacitor, or tap a static VAR compensator... when voltage gets low in a trailer battery, it becomes less efficient... period. While, even on the power grid, Watts and Amps aren't perfectly interchangeable, but when you're talking about hundreds of thousands of watts at any given time, the difference is negligible. And then there's inductive and capacitive reactance. DC really is much simpler... my brain just needs to adjust. Much appreciated Howard!

This is good stuff! Thanks everyone. I'm really interested to see if there's a difference in either capability or longevity if I parallel the batteries or if I connect them separately, via a transfer switch, to the inverter. Time to dust of the old calculator I'm also starting to wonder what effect the ambient temperature will have on the charge state? I've always been under the impression that batteries don't do well in the cold. That voltage curve must bend a little harder in <32° temps?

[NCW_Wander]

oh, Guest , A lot of what you said went over my head... But you can bet that I won't spend a dime until I understand exactly what you're talking about. I'm about to pepper my google history with keywords like "prismatic" and "cylindrical"!!! Thank you!!!

[howson]

That voltage curve must bend a little harder in <32° temps?

Absolutely. Battle Born even sells a version of their battery that has a built-in heat blanket to ensure it will work (and charge) in cold weather.

My school instructor had a very simple fix for the effects of cold weather on batteries: head south.

[Guest]

Another option is to install batteries in an area that we ourselves find comfortable and there will be no issues. Lithium batteries normally do not vent so they can be installed in any position in the main living area to protect from temperature extremes. For our early spring and late fall boondocking trips where temps can drop below freezing at night, the pass-though provides enough heat transfer to keep our battery plenty warm. If we winter camped I might install them under the bed or in a cabinet. Battery temps can also be monitored with the Victron BMV-712 if there are any concerns. Heat kills batteries also but I would like to be in the south right now. Its cold!

Jim

[TedS]

Remember, too, that for resistive loads as voltage drops so does current flow. Resistive loads include electric heaters, lights and dc motors. Lower voltage drives less current through resistive devices, elements. A 1500 watt heater does not deliver constant 1500 watt output with dropping voltage and resultant lower current. There is less heat produced as voltage drops.
DC motors run slower and produce less power as voltage and resulting current drop. Slides run slower with lower voltage.
AC motors are a different animal. They are not a simply resistive load. Current will increase as voltage drops.

[Teamjd]

There is actually an upside to buying two 200Ah batteries instead of one 400Ah... usable current.
Most Lithium replacement batteries have a 100-120 amp max output before the BMS cuts off.
If your actual usage is below this then either would work, but two 200Ah batteries gives you 240-ish usable amperage.
In the rare event that one battery craps out, you still have power. They are pretty reliable though.
The other benefit is if you plan on using an inverter. One battery (120A output) pretty much limits you to a 1500 watt inverter.
Two batteries will let you use a 3000 watt inverter.

PS - one more thing... with the proper charger, two batteries will take less time.
Most Lithium's have a max charge rate of 50A.
Two batteries in parallel could be charged at 100A, so half the time.

[Guest]

NCW_Wander This battery has caught my attention where they use prismatic cells BUT they are UL certified. With a price of under $400 for a 100ah battery with a 100amp continuous discharge this battery would be worth a try. Personally I trust my own judgement and my Victron BMV-712 over any imported BMS where I never allow the BMS to come into play. Having stated that, I believe this battery may not have a low temp cutoff which does not matter if you do not winter camp. If you do, locate them inside the rig and charge after monitoring battery temps.

https://www.amazon.com/CHINS-LiFePO4...30&sr=8-3&th=1

They also have another model with a built in heater (not needed IMO) and a built in monitor app for under $700.

Amazon is also offering a 4 year warranty on these batteries where at this price, it can't be beat.

Another thought on Prismatic cells is that if one goes bad, the pack will not function. However, replace the cell with another (preferably from the same maker) and you can re-build this battery. Cases can also be found separately. The consumer cannot service cells individually with a cylindrical cell battery.

A thought on cheap affordable lithium packs. They all come from China be it wholly or assembled here with cells and BMS from China. Monitor these yourself or install a relay on the Victron monitor and this is a good affordable option with UL certification.

Found this video on the Ampere time from Will Prowse as well.

https://www.youtube.com/watch?v=FQUhjDkQY5Q

Jim