Adding to a Renogy Battery Bank

[DaveP]

I currently use four Renogy Smart lithium iron phosphate 100 Ahr batteries in parallel in my system. I would like to add two more Renogy batteries, but Renogy says that I cannot add a fifth and sixth battery because the battery's cell auto-balancing circuitry will only handle four batteries.

Anybody know of a way/have any ideas on how to get around this limitation?? (External circuitry or whatever?)

Thanks!

[ZeGermans]

I’d not parallel more than 4 lithium batteries either. For one you have to really make sure that all cables from charger / load to each battery have the same resistance to be able to balance them out enough, if not and the BMSs try to balance you are probably be ending up in a ping pong game… you really have to add a good busbar
The other thing, one battery shorts all others discharge into that shorted battery we’re talking 100reds of amps! Class t fuses…

I’d not do it either… if you need more power think about upping your system to higher voltage and other batteries.
For reference I have 15kwh in two batteries at 24v.

[ZeGermans]

And electrically I’d prefer one 48v bank but I chose to go the 24v route only to have redundancy in case I have a damaged cell or something… although on the other hand it doubles the chances for a BMS failure… but I’d never consider more than 2 batteries in parallel…

[Wazbro]

You could add the other 2 batteries with DC to DC chargers (one to charge them and one to get the power from them or a battery switch). That way you could use the new batteries as a reserve with just 1 DC to DC charger and a battery switch or 2 DC to DC chargers for more capacity, just might not add any real time assist for a big load like running air conditioner.

I'm not saying it would be worth doing it since I don't know of a way to have it work well without manually managing it. Probably only good for occasional reserve capacity.

[Taco Joe]

Why not swap out 2 of the 100s for 2 200s, or better yet, your 4 100ah for 3 200ah. For me the 200s fit under the bed. I have done very well with 400ah total and 500 watts solar on the roof and an extra 60 watt portable panel to help out if shady. You didn't mention if/how much solar you have. You could always repurpose the 100ah batteries for your house, garage, shed etc.

[DaveP]

Originally Posted by Taco Joe

Why not swap out 2 of the 100s for 2 200s, or better yet, your 4 100ah for 3 200ah. For me the 200s fit under the bed. I have done very well with 400ah total and 500 watts solar on the roof and an extra 60 watt portable panel to help out if shady. You didn't mention if/how much solar you have. You could always repurpose the 100ah batteries for your house, garage, shed etc.

Hi TJ,

I am trying to find a way to use what I have and add on. This would possibly avoid having my DW shoot me for spending even more $$s. I have 600 watts of portable solar (Renogy suitcases), but my energy storage capacity gets kind of short in the cold months with short solar days in the Rocky Mountains. I use a bipap machine and the portable oxygen generator uses quite a bit of power (along with the furnace, etc.). I usually top off the batteries with my two Honda generators in parallel if the solar day falls short, but I would love to get three full days of power without any charging (solar or otherwise) which the additional 200 Ahrs would give me.

I am beginning to think this is a pipe dream, and I'll just have to live with what I have.

Thanks for everyone's inputs.

[Taco Joe]

I generally do upgrades in phases, to save on cash and complexity (and mostly stay below wife radar). If it was me, I'd add the Renogy 200Ah battery (mine are the bluetooth version) if it fits and the cabling wouldn't be hugely different than current ones, and put it on an A/B switch with your other batteries as reserve. Next upgrade, add DC to DC charging from TV alternator to new batteries. If needed eventually swap 2 of your 100s for a 200 and combine everything or add the 2nd DC to DC charger as suggested above.