Wednesday, November 30, 2022

Battery Project - Part 1

 - Now starts the planning process for the battery installation. Since the battery bay is an uninsulated compartment, I will be building an insulated box for them. 

The bottom of the battery bay is sturdy metal and Home Depot has 1” rigid insulation in 2’x2’ pieces. I think that’ll work for the bottom of the box. A piece of 1/2” plywood will distribute the load onto the foam. The box itself will simply be 1/2” plywood with 1/2” insulation inside with the same construction for the top. 

I’ve identified most of the cables shown in the first picture and I want to relocate a couple of them that will be hard to access once the box is in place. The large, cylindrical relay on the right will be removed and replaced with a DC-DC charger. This relay is energized when the engine is running to allow the engine alternator to charge the coach batteries. The alternator is rated at 160amps and the DC-DC charger will limit the current to 40amps. The internal resistance of LiFePO4 batteries is very low and it will max out the alternator (burning it out) and possibly exceed the max charge rate of the batteries (70 amps each). The other purpose of the relay is to “jump” the chassis batteries in case they are dead. 

 - The batteries arrived already, three days before they promised. I checked the voltage on them and they are both partially charged. The batteries also have Bluetooth built into the BMS (Battery Management System) so I can see the individual cell voltages and the internal temperature. This is an unexpected feature. The next screenshot shows how the battery shows up on the phone screen.

At the top of the screen is the SOC (State of Charge) but it won't reflect reality until after a couple of complete charges. There is a switch for heating but I didn’t get that option. At the bottom are the individual cell voltages. Pretty cool! 

The first task was removing the old batteries and wiring them back up to the RV so we still have 12V functionality. Another RVer here in the park loaned me a set of jumper cables so I could temporarily power the RV off of the old batteries. The battery bay has a lot of rust on the bottom where the flooded lead acid batteries were sitting so I'm going to paint the floor before starting to build the battery box. The rust is just on the surface and the Rustoleum paint that I already have says to just remove the loose rust and clean with soap and water. This afternoon, picked up a drill mounted wire brush and used that do get rid of as much of the surface rust as I can. Tomorrow, paint. 


  1. Wow, batteries with built-in bluetooth for their BMS...heck, batteries with BMS!

    1. Batteries with Bluetooth. Who would’ve thought that would be a “thing”.