Question on switching to LiFePO4 batteries.

mbloof wrote:

Sterling1 wrote:
I'm going to replace my 2 lead acid batteries in my Bigfoot truck camper with two 100ah LiFePO4 batteries. I've previously installed a 4 way battery selector switch to allow me to keep one of my batteries at a high enough charge level to start my generator (they are run in parallel). However, this won't be necessary (and probably won't work) with the lithium batteries and I will probably need to have it at the Both position to start my generator.

My question is is can I damage the batteries if I switch to the Both position when one battery is low and the other battery is fully charged?

In a word: No.

A battery is simply a energy storage device.

No matter what "type" or chemistry the batteries are if they have the same nominal voltage (IE: 12V) then the following would be true:

Battery #1 is 12.5V and Battery #2 is 13.5V and you hook them both together in parallel along with a load. What happens?

The load will draw current from BOTH batteries but since Battery #2 is at a higher charge voltage than battery #1 some of Battery #2's energy will flow to Battery #1 until such time BOTH batteries have the same charge voltage.

If you simply hooked a not-so-much charged battery up to a fully charged battery without a actual load the "not-so-much charged battery" would still be a load to the fully charged battery until such time that both batteries have equal voltage.

So can you can see the 'wasted' energy/charge being used for the lesser charged battery?

This is why it is generally recommended that to use two or more batteries in parallel they ought to be the same Brand+type+age+capacity and charge level so stored energy is not wasted charging the other batteries in the bank.


- Mark0.

You're forgetting about the BMS and the electronics in it.

The "best practice" recommendations are to fully charge each battery separately and then let them rest for 1/2 an hour. Then if the open terminal voltages are within 0.2V then it's good to hook them up.

LiFePO4 is a different animal and while it has a few things you can't do like you did with your old fifty buck Walmart special, it isn't really that hard. little things like using a capacitor to preload your inverter circuit before you hook the batteries to it, on a new install, is it necessary probably not, but it does reduce the chance that feedback from a spark will take out any electronics.

even things like making sure you can parallel it, some can't, some have 2 battery restrictions some have 4. same goes for series installation, do the homework. Also, while some do, it isn't recommended to mix LFP batteries of different types or different sizes. different brands may use different BMS units that may or may not play well with each other. in the case of different sizes, the smaller one will cycle deeply every cycle and wear out long before the other one.