Connecting a Lithium deep cycle battery in series with Flood Acid deep cycle battery?

DIY Tin Can

New Member
Joined
Oct 9, 2021
Messages
4
I am planning on purchasing a 400W HQST 40A MPPT system with possibly a 2500 watt pure sine inverter. I just purchased 4 - 3.2v 176AH lithium cells to run my travel trailer. I was curious I am replacing my two super Start 27DCMJ Deep Cycle Marine batteries with that one 176AH Lithium 4 cell battery, if I needed more capacity could I connect the lithium battery in series with the flood acid deep cycle marine battery for more capacity? or do I have to connect lithium to lithium? Will, by the way, I think your youtube/ website is really very help full, you explain things in a manner that a less than normal/ less educated person like myself can follow. thank you for all you do.
 

MurphyGuy

GOD ALMIGHTY
Joined
May 20, 2020
Messages
1,044
Series connections change voltage
Parallel connections change capacity (amp hours)

Connecting batteries of different chemistries in parallel requires a battery isolator/combiner.. and you need separate charge controllers.
 

DIY Tin Can

New Member
Joined
Oct 9, 2021
Messages
4
I apologize I miss spoke. I was wondering if they could be connected together in parallel?
 

MurphyGuy

GOD ALMIGHTY
Joined
May 20, 2020
Messages
1,044
I apologize I miss spoke. I was wondering if they could be connected together in parallel?

Yes, but you need a battery isolator to do it.

The reason is that the two batteries have different charge and discharge profiles. Sure, if both batteries are at the same voltage and you only want to draw a tiny bit out of them, and that draw is within the specs for both batteries, then it wouldn't hurt.. But that's never really the case. Charge and discharge limits are going to be different and they must be isolated from each other for that reason, even though they are feeding the same load and working together.

Battery isolators are usually under $100.
 
Top