Lithium battery upgrade (from lead-acid batteries)

[Ernrays]

Hopefully, someone in the forum can help me with an upgrade so I don’t use my normal method (aka, trial and ERRORS).

Our 2008 Montana Mountaineer is almost as old as I am but in much better condition. We use it 4 months a year at a lake at 8,900 feet in an RV Park with full hook ups. I had two lead-acid batteries (in parallel) in the 5th in case the shore power goes out. The converter kept the two 2016 lead-acid batteries at full charge but one of them recently developed a dead cell, and I image the other one will bite the dust soon (they don’t owe me a thing).

I want to install in the 5th a 100 Ah Ionic LiFePO4 battery that I already have. It has the same power output storage capacity as the two lead-acid batteries had together. It weights less than half as much and recharges much faster.

I have some questions before I try to install it:
1. I measured the power output of the current converter; it is about 13.5 VDC. The LiFePO4 battery needs about 14.5 VDC to reach full charge. So, I think I need to replace the converter with an Ionic Charger. Where is the converter located in our rig? It’s so old that I haven’t found the information on the web yet.
2. If I’m not on shore power, the power output from the lead-acid batteries was 12.9 VDC. The power output from the Ionic Battery will be 14.1 VDC. Am I going to cause some other problem in the 5th due to this voltage increase, like the blower motor on the furnace or the water pump?
3. This last question probably belongs to the manufacturer, but maybe the answer resides in the forum members. Can I continuously charge the LiFePO4 battery at 14.5 VDC without causing it problems? I think its Battery Management System handles that issue, but it’s a guess on my part.

Any help would be appreciated.
Thanks,
ernrays

 

[Carl n Susan]

1. I measured the power output of the current converter; it is about 13.5 VDC. The LiFePO4 battery needs about 14.5 VDC to reach full charge. So, I think I need to replace the converter with an Ionic Charger. Where is the converter located in our rig? It’s so old that I haven’t found the information on the web yet.

I am guessing but you likely have a WFCO power panel and a stand alone converter. It will be located very near to the power panel, probably behind it. Depending on the location of the power panel, you can either remove the panel (there is slack in the wires) or access it through from the pass through compartment (by removing the back wall - 6 screws or so).

Your current converter may, or may not, be a "Smart" converter with 3 or 4 stage charging. If it is, then the Boost mode provides around 14V of charge. It will not fully charge your lithium but will get it up to around 80%

2. If I’m not on shore power, the power output from the lead-acid batteries was 12.9 VDC. The power output from the Ionic Battery will be 14.1 VDC. Am I going to cause some other problem in the 5th due to this voltage increase, like the blower motor on the furnace or the water pump?

No, the 12V devices can handle power variations past 15V.

3. This last question probably belongs to the manufacturer, but maybe the answer resides in the forum members. Can I continuously charge the LiFePO4 battery at 14.5 VDC without causing it problems? I think its Battery Management System handles that issue, but it’s a guess on my part.

As I understand it, lithium batteries don't really like being at full charge all the time. It will shorten their life. You can maximize the lithium battery life by keeping it between 20% and 80% State of Charge (SOC).

Given you are on shore power most of the time and only use the battery in the event of a power failure, I would be tempted to replace your current batteries with AGM ones. They don't loose water, and your current converter is adequate. I don't see a need for the extra expanse of a lithium battery and a new converter for your usage. But as you have the lithium battery already, try using it with your current converter and see how it works.

 

[Daryles]

Excellent article on Lithium batteries

How to find happiness with lithium batteries
https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/

 

[MandK]

I don’t know if this is best practice, but from what I have read, using your current charger for your lithium battery may not be a bad option seeing as how you are setting on shore power.
I ran mine on my charger’s LA profile for the month of December and it never went below 98%. I was actually hoping it would go lower to about 80-85%.
I ran it on the LI profile for January up until a few days ago and it floated at 100%, as it should, but the cell balance didn’t look as happy (but still in spec) as it does on LA.
So as long as we are going to be hooked up to power for several months, I’m using the LA profile. It’s back on LA now and everything looks as good as it did in December.
December picture LA. January picture LI.
My Victron 712 confirmed these Bluetooth figures.
Ymmv.

 

[Ernrays]

Carl,
Your suggestion is going to save me a ton of time and expense. Thank you! I'm going the AGM route for the 5th. I have another use for the 100 Ah Lithium on the boat (power the fish finder and stop drawing power from the starter battery).
Thanks again!

 

[MandK]

Carl,
Your suggestion is going to save me a ton of time and expense. Thank you! I'm going the AGM route for the 5th. I have another use for the 100 Ah Lithium on the boat (power the fish finder and stop drawing power from the starter battery).
Thanks again!

Seeing as how you have another use for the lithium battery, I think that is a good choice. Good luck.

 

[Ernrays]

Great teaching article! It provided answers to several questions that I have had and provided some additional "need to's." Most of all, it explained the why's. Since I use two LFP batteries in series to power my bow motor, it helped me see where to dodge some issues, like cell balancing (occasionally charge the batteries when they are in parallel). Thank you for providing the link!

 

[Daryles]

Just an FYI,
based on that article, I switched to lithium batteries five years ago and STILL have the original Progressive Dynamics FLA converter.
I have added solar (set to Lithium profile) so when we are boondocking, the batteries get a full charge. When on Shore power I turn off the solar MPPT Charge controller and just let the converter handle it at a lower charge voltage (longer lithium battery life).