Automatic transfer switch between batteries

[French_guy]

Hello

Assuming I have 2 x 12V batteries (A and B) that are different types and I don't want to have them in parallel (One is a new 100Ah LFP and the other one is an "older" 75Ah AGM but in good shape)
Is there an module or circuit that would automatically switch from A to B when A has reached a specific voltage (DOD)?

 

[12VoltInstalls]

Hello

Assuming I have 2 x 12V batteries (A and B) that are different types and I don't want to have them in parallel (One is a new 100Ah LFP and the other one is an "older" 75Ah AGM but in good shape)
Is there a module or circuit that would automatically switch from A to B when A has reached a specific voltage (DOD)?

You could do that with a $20 eprom voltage controller relay switching some humongo relay durable enough for the amps. But is it worth it?
I’d probably just parallel them or buy another 2400Wh LiFePo battery