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Old 03-21-2023, 12:39 PM   #1
2017 Forester 3051s
Join Date: Aug 2017
Posts: 47
Switching from LA batteries to LI

I have a 2017 Forester 3051s. 30 amp shore. It has a Progressive Dynamics power supply with LA 60amp converter. I talked to Progressive and was told I just need to change my converter to the LI version of my converter and they gave me the part number I needed.
But I have a concern. It seems to me that the 12 volt house system ties into the 12 volt engine system. Do I need something to protect my 12 volt LA battery in the engine compartment and my engine altinater? I don't want to blown stuff out.
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Old 03-22-2023, 05:52 PM   #2
Old man RVer
Join Date: Sep 2020
Posts: 243
Interesting question

As of this reply, 110 folks have viewed your posting but none have replied. Your issue appears to be whether your house battery charger also charges the engine’s battery and, visa versa, whether the vehicle’s alternator charges the house batteries. Since you want to have dissimilar batteries (Li-Ion for the house and lead-acid for the engine) that’s a damn good question.

Since no one has offered a suggestion, let me take a stab - test the house batteries at rest — nothing charging them. Start the vehicle and test again. Any rise in battery voltage would indicate charging taking place. That is, the engine’s alternator is charging the house batteries. This is common, to help keep these batteries charged while traveling.

Now, with the engine off, measure the engine battery’s voltage. Do not have shore power plugged in. Then hook up shore power (120 volt) and go test the engine battery. Again, any rise in voltage would indicate charging, this time meaning the house charger is charging not only the house batteries but the engine battery. This is less common.

With this knowledge we can better determine how to charge your dissimilar batteries.
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Old 03-22-2023, 08:23 PM   #3
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Join Date: Jul 2017
Location: North of Seattle, WA
Posts: 16,142
Charging dissimilar batteries will require either a DC-DC charger or a Li-Bim (lithium Battery Isolation Manager). A DC-DC charger will provide a lithium charge profile to the new coach battery independently from the charge profile of the alternator regulator. A Li-BIM will turn charging from alternator on and off in pulses so alternator doesn't overheat due to the higher current draw by the low internal resistance of a LiFePo4 battery.

I have a Travel Trailer which is different enough I'll leave the solution to those who have Motorhomes. The unique issue with motorhomes is the issue of charging starting battery while shore power is plugged in ascwell as ability to utilize the emergency start feature most MH's have.

I use a DC-DC charger and don't worry about truck battery. If I was concerned I'd just permanently wire a good battery maintainer and plug it in whenever shore power is available. Doing that would also negate the need for an emergency start button.
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Old 03-22-2023, 09:25 PM   #4
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Join Date: Sep 2017
Posts: 134
LiBIM fits in some FR RFVs

I needed the LiBIM in my RV so that the engine alternator would charge my LiFePO batteries while driving.
If your BCC looks like mine, it's a pretty simple swap.
2018 Sunseeker 2400R MBS (w/dinette)
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Old 03-23-2023, 12:05 AM   #5
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You will want some type of battery isolation. On my class C with the E450 chassis, I went the DC-DC charger route. I bought the Renogy 40amp model and it has worked good for me.
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batteries, switch

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