Once in a while we post slightly off topic findings that we think will be interesting/unique information for readers. This post is about the very popular Renogy LiFePo battery with built-in Bluetooth. Even though we don’t provide solutions for these batteries yet, we have recieved enough guestions about them that we got curious about what seems to be the common failure. This specific post shows the guts of a RBT100LF/P12-BT-US version, but there are versions that will have similar components. These batteries are commonly used in off-grid applications to provide power to DC and AC devices using an inverter.
Failure Mode
The “dead battery” – This is when there is no output voltage, no bluetooth connectivity and the battery will not charge. We don’t recommend repairing these batteries due to a fire risk, We decided to get into to understand the battery a little better. Note that we kept a fire extinguisher near and will not put this battery back into rotation even after fixing the failed part.
Getting Into It
Not a lot of help we can provide here. We cut, heated , cracked at the plastic and finally got the top to come off. Send us a message if or make a comment if you find a better way to open a battery like this. We will recommend it here.
Getting the top off is touch
BMS Failure, Cells or Wiring
In modern LiFePo batteries, you can break it down into three parts, Cells, Wiring and BMS. Once the top is removed, the basic troubleshooting can start. Before getting started it is interesting to note this is a pretty high-quality battery, Prismatic cells..solid. Epoxy molded to keep things from moving around..solid. No corrosion or dust since the case is sealed from the elements..not much to complain about.
If you took a good look at the picture above, you will notice that the voltage measurements and the wiring look good. Since the cell voltages add to 13.2V and we don’t see any loose wiring, the likely culprit of the failed battery is the BMS. There is a lot of information on the internet explaining what the BMS does, but basically, it makes sure the cells are balanced and it cuts off the connection to the LiFePo cells if there is a fault condition like too cold, cells are under-voltage, charger is trying to overvoltage the cells. In this case, the BMS seems to be keeping the cells disconnected even though there are no real fault conditions.
What BMS Did They Use?
Well, the big clue are the red heat sinks. To get to get it the BMS the way we did involved more caveman technics. A dremel cutting tool is how we did it.
Again, please let us know if you have a better way to get to this. With some more cutting and prying, we got the BMS out. Sure enough, it is a standard Daly 4S 50A charge/100A discharge BMS you can get almost anywhere. We will follow up this post will a schematic extraction of the BMS. Why? No good reason. These are so cheap it doesn’t make sense to try and repair it, but we will do it to understand why they are failing. If you have read this far and actually took apart your battery to find a failed BMS, just buy a new one for about $50.
Not sure how long the link will be active, but this is the one…
Hope geeking out on a LiFePo battery was fun for you. It was for us, because we love digging deeper. If you have any questions or general comments please email us at info@comvolt.com.