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Needing to replace RV battery bank, have several questions regarding prebuilt and DIY LFP's. ?

JWes

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Dec 27, 2021
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My off-grid RV desperately needs its house batteries replaced. I've been using four 6v golf cart batteries paired at 12v for the last decade and want to upgrade to lithium because it seems like I can save weight, gain longevity, and Gain energy storage for just a couple hundred extra bucks. I have a 1740W solar array, two Midnite Classic 150 charge controllers, and a supercapacitor bank to help with starting the air conditioner. I'd like at least 200Ah @ 12V with the 200A BMS to handle the microwave, generator starting, and 5000 btu window air conditioner startup surge and preferably keep it under $700... Ok going to $800 or more for extra capacity to run air conditioner for longer than a couple hours after sundown. So yeah, trying to avoid the price of premium packs like SOK if these cheaper packs work well enough.

Regarding prebuilt batteries:
1. I'm trying to compare the Zooms ($690 with coupon!), Chins ($700), and Ampere Time ($740 with coupon), each with the 200Ah @ 12V with the 200A BMS... are they internally all the same? All no low temp sensors? Are there any similarly priced/size batteries to compare with good internals?

2. Do either of those three offer better tech support than others? I couldn't find a website for Zooms battery; Chins and Ampere Time had sites but overseas numbers.

3. How do I figure out how to charge them with my Midnite Classic 150 chargers? Can I expect them all to come with comprehensive charging parameters?

4. With the prebuilt batteries, do I have to do and top balancing, bottom balancing, capacity testing, or anything else before dropping in to use?

5. On one of Will's videos, I think he recommends cycling usage of lithium batteries between 20-80% (another youtuber recommend 10-90%) state of charge to get the best longevity; is this correct? How do I achieve this with the Midnite Classic 150 charge controller? I do have a shunt and amp hour meter (Midnite wizbang jr)... will it use that? Or are there other/better ways to keep it in between 20-80% state of charge (like voltage)?

6. In this video, Will mentioned balancing cells ever 6-12 months...
Do you really need to do this if the battery has a BMS? Do some BMS's not do balancing, and how would I determine if it does or doesn't? I was under the impression that LFP's were largely maintenance free. How do you know if cells need rebalancing? Do the Zooms, Chins, or Ampere Time have a way to interact with the BMS since I don't think they have bluetooth? How would I determine a cell or other internal failure on these after (hopefully) several years if the BMS cannot be connected to? Do these prebuilt batteries come balanced from the factory?

Looking at DIY batteries...
7. Are there any other vendors in the US that y'all recommend besides this site? http://www.powerwholesale.net/Wholesale-Discount-battery-lifepo4-battery_c34.html I'd prefer to avoid the wait of overseas shipping, being without electricity right now is stressful.

8. Is it even possible to beat the overall price of the above prebuilt batteries? Seems like after adding BMS, busbars, temperature sensors, nuts/studs, balancer(s?), casing, power supply to balance, plus labor to balance, test, build, the DIY route seems more costly, no?

9. Do I need anything else for a DIY battery that's not listed above in question #8?

Thank you all so so so very much... this has been a stressful educational journey and I'm so grateful for any help! If this is going to be as easy as dropping in the cheaper Zoom's battery and resetting some voltage and times on the charge controller, that'd be a relief. I am worried about no low temperature cut off, but Midnite promises that they will have that addressed in new firmware next year, guess I'll just have to disconnect stuff during a freeze until then (not too often around Austin TX).
Blessings ??️✌️?
 
3. How do I figure out how to charge them with my Midnite Classic 150 chargers? Can I expect them all to come with comprehensive charging parameters?

They should have at least absorption voltage. 14.4V absorption and 13.6V float are good numbers. Tail current of 0.05C or 10A.

4. With the prebuilt batteries, do I have to do and top balancing, bottom balancing, capacity testing, or anything else before dropping in to use?

Not in that sense. If you're going to wire batteries together in series, all must be charged to full before they are placed in series.

5. On one of Will's videos, I think he recommends cycling usage of lithium batteries between 20-80% (another youtuber recommend 10-90%) state of charge to get the best longevity; is this correct? How do I achieve this with the Midnite Classic 150 charge controller? I do have a shunt and amp hour meter (Midnite wizbang jr)... will it use that? Or are there other/better ways to keep it in between 20-80% state of charge (like voltage)?

This is stated often, but it's not a simple matter, nor is it often worthwhile to pursue. Simply don't discharge them below 3.0V/cell and don't charge any faster than you have to. If you can tolerate 5+ hours of charging, an absorption voltage of 13.8V will take them to 98%+ SoC slowly and gently thus minimizing stress on the cells and maximizing cycle life.

Note: for generator charging, you'll want to go to 14.4V, otherwise, it will run longer than desired.

6. In this video, Will mentioned balancing cells ever 6-12 months... Do you really need to do this if the battery has a BMS?

No.

Do some BMS's not do balancing, and how would I determine if it does or doesn't?

Most do.

I was under the impression that LFP's were largely maintenance free.

Usually.

How do you know if cells need rebalancing?

You don't.

Do the Zooms, Chins, or Ampere Time have a way to interact with the BMS since I don't think they have bluetooth?

No.

How would I determine a cell or other internal failure on these after (hopefully) several years if the BMS cannot be connected to?

Disassemble the battery and manually measure cells.

Do these prebuilt batteries come balanced from the factory?

In most cases, they seem to behave as though they are.

Looking at DIY batteries...
7. Are there any other vendors in the US that y'all recommend besides this site? http://www.powerwholesale.net/Wholesale-Discount-battery-lifepo4-battery_c34.html I'd prefer to avoid the wait of overseas shipping, being without electricity right now is stressful.

Search the site. I can't make recommendations.

8. Is it even possible to beat the overall price of the above prebuilt batteries? Seems like after adding BMS, busbars, temperature sensors, nuts/studs, balancer(s?), casing, power supply to balance, plus labor to balance, test, build, the DIY route seems more costly, no?

Yes, but not by much from the cheapest brands. You'll be out about $750 total for a 280Ah battery.

9. Do I need anything else for a DIY battery that's not listed above in question #8?

Sounds like you have it covered.
 
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