Oops - Start Batteries Fried

[markpj23]

During COVID I had to replace the 8 6V GC2 batteries in our RV. The only ones I could get at the time were FLA units to replace the solid-state units that had expired. Repair shop installed the new units and I set the inverter / charger profile to Lead Acid battery type. All is good..... until now as I realize that my two group 31 start batteries were AGM units. Turns out that FLA charging profile is not great for AGM units (should have checked this..... ) so now my 2 year old start batteries are history.
The house batteries are still good of course (although I really hate having to clean those terminals every 6 weeks or so and do not want to add 2 more FLA start batteries to the mix). Then it dawned on me that I could replace the start batteries with AGMs, add a DC - DC charger and set the RV's inverter / charger back to AGM profile and just let the DC - DC charger handle the house batteries.
The drawback would be the lower charging rate from the DC - DC unit (60A) as opposed to the 100A I get from the inverter/charger. Thinking further, I could also choose to set the inverter/charger profile back to AGM for all batteries and live with the lower state of charge on the FLA house batteries. I am not ready to replace the house batteries yet as they are still doing the job (may eventually go to LiFePOs come replacement time).

Which of my three options do you think I should choose? 1) buy FLA start batteries; 2) Buy AGM start batteries and add a DC-DC converter; or 3) Buy AGM start batteries and just set the existing inverter/charger to AGM charge profile.

 

[time2roll]

Option 3 gets my vote. Can disconnect the AGM during an equalization every 4 to 8 months depending on use.
If you are cleaning terminals that often the voltage might be a bit high or the electrolyte level is a bit high in the cells.

In time I would replace the GC2 with lithium.

 

[Rocketman]

Look forward…. What are your eventual plans? And how are you going to get there?

If you go lithium for your house bank, then you will need the Dc-Dc charger.

I put in AGM starter battery on my MotorHome. It sits right above my diy lithium battery bank - i really like to no acid leaking feature on AGM’s - to me it’s worth the cost difference of the AGM battery.

Remember you probably have TWO charge paths… When the rig is plugged into shore/generator - the inverter/charger is charging. When the rig is traveling the alternator is running. You need to account for both power sources for both batteries.

I separated the two systems…
Chassis is charged by alternator and one solar panel on a 100/20 mppt SCC.

House is charged by:1400w of solar, inverter/charger when on shore/generator, and a Dc-Dc 30a charger from the alternator.

Good Luck

 

[yodamota]

Id buy FLA start batteries.. I have FLA start batteries which are from 2013.