2P16S or Two Separate Batteries?

[Brett V]

History: I built a 16s battery for my Growatt using an Overkill 100 amp BMS and 230 amp EVE cells. It works wonderfully but I wanted more capacity so I purchased another 16 of the same EVE 230 amp cells. I also picked up another BMS, Class T fuse holder, shunt, the whole enchilada...with the intention of building another identical battery and then paralleling them at a common point. I'm familiar with the critical importance of resistance and cable lengths when hooking up battery strings in parallel but my experience in doing so is with lead batteries and it just never seems to work as intended. Maybe Lifepo4 behaves better in this scenario? I don't know.

Dilemma: Having two separate batteries each with their own BMS has the advantage of redundancy but I run the risk of uneven load sharing. Building one big 2p16s battery eliminates that problem and does simplify the build considerably, but I will lose the redundancy and the ability to monitor each and every cell as an individual. I'm looking to the group for thoughts yay or nay either way and realize there is no absolutely right or wrong answer. Also worth noting, these batteries will spend most of their life floating around 95% SOC as I use this for a whole house UPS and don't regularly cycle them. I may get some panels in the future and exercise the Growatt daily depending on how the future of net metering and electric prices play out, but that's not in the plan for now.

 

[Struc]

realize there is no absolutely right or wrong answer.

Glad you stuck that in there.... Really only opinions, but I'm of the 2 battery camp. I like monitoring every cell, and I like the redundancy. It costs a little more, but looks like you already bought everything anyway.

As far as "behaving" correctly.... there are plenty of videos out there on paralleling batteries - even of different capacities, so I wouldn't fret too much. Once it's set up, just make sure it is behaving properly (in your case, close to equal amp draw on each bank). Pretty sure even Will has a video out there of a bunch of different batteries he had hooked up, and each bank was drawing amps proportionately to the size.

 

[HRTKD]

Another vote for the two battery implementation. Monitoring, redundancy and configuration. Creating a separate compression fixtures for a 16s battery is easier than 2p16s.

I have no problem with the balance between my two 4s batteries.

 

[John Frum]

I vote 16s2p.
With 2p16s you get half the balance current and the same charge/discharge current as you currently have.

With 16s2p you get the same balance current and 2x charge/discharge current.
Plus fault tolerance.

 

[Brett V]

I guess I'm leaning toward the 16s2p. My first battery was built in a truck toolbox and worked out really nice. I figured I'd get another and make the same identical battery but with my mounting location in the garage, keeping the cables the same length was a problem. I found a larger toolbox that will give me enough room to line up two rows of cells next to each other. That simplifies the build considerably.