Is it safe to mix battery types with EG4 hybrid inverters

[the detective 🔍]

I’m setting up a full home backup and offset system in a rural area and recently picked up two refurbished EG4 6500EX hybrid inverters along with one EG4 12.3kWh wall mount battery to get started.

I’ve read about some early hiccups with these inverters but it sounds like the newer firmware has improved things so I’m moving forward with the install in the next few weeks.

My question is about expanding the battery bank down the road. Do I need to stick with the same EG4 capacity or can I safely mix in other 48V options? I already have a couple of 48V 100Ah rack batteries on hand and a neighbor is offering me a 15kWh wall mount also a 48V, at a good price. Would combining these with my EG4 cause issues with balancing or cycling or is it workable if managed correctly? Thanks!

 

[Princess_Lora]

I would stick to matching battery specs as much as possible. If your neighbor’s 48 V battery is close in voltage and chemistry, you can test combining them, but always isolate and test first. Use fusing and good balancing wiring so one battery doesn’t drag the others.

 

[LordRobert]

Even though they’re all 48V, the chemistry and resistance can be slightly different, and that’s where balancing problems start. You might see one battery hitting full charge before the others, which kills efficiency long term. If you’ve got separate breakers and monitoring, you could still run them, just not in the same parallel bank.

 

[fullych4rg3]

the most important thing is the chemistry. since your EG4 is LiFePO4, you must only mix it with other LFP batteries
if your neighbor’s 15kWh unit is a different lithium chemistry, the voltage curves won't match, and one battery will constantly try to charge the other, leading to high heat or a BMS shutdown
if they are both LFP, it's doable, but not ideal

 

[Alan]

Workable sometimes, but you have to think in terms of matching characteristics, not just matching 48V. If you parallel different batteries, the one with the lowest internal resistance and highest allowable current tends to do more work and age faster. The neighbor 15kWh wall mount could behave very differently than your EG4 wall mount and your 48V 100Ah racks. If you do it, set identical charge voltages, conservative current limits, and make sure all batteries are at similar state of charge before paralleling. Also keep cable lengths and bus bar layout symmetrical.