Question- Pairing batteries in parallel

[Liam M]

Hi,
Brand new here, and really loving the community here.
I’m setting up my first ever off grid system.
I first purchased a durdc12-100p AGM 100ah battery a couple weeks ago, and wanting to expand as I go.
I bought this battery because it was available locally, but It’s expensive ($289)
I’d planned to purchase cheaper batteries (same specs sold for <$200) to add to it in parallel, but have since read that mixing brands is not recommended.
Am I stuck buying more of the same expensive battery?
Any suggestions?
Thanks!

 

[Liam M]

Sorry, here is a link to the battery I bought

https://www.batteriesplus.com/produ...MI3P3O1rK86gIVJz6tBh2hwg6tEAQYASABEgLZk_D_BwE

 

[gnubie]

You can pair different brands in parallel but try to keep them comparable quality and rating, ie don't pair a 1000 amps rolls with a 50 amp yumcha. You must ensure they are the same chemistry, design and voltage too. Don't pair an AGM with a flooded, nor a lithium with a lead acid, nor an AGM with a gel etc. Pairing a 12 and 24 voltage battery would be .... interesting .... from a safe distance.

 

[clopez88]

You can pair different brands in parallel but try to keep them comparable quality and rating, ie don't pair a 1000 amps rolls with a 50 amp yumcha. You must ensure they are the same chemistry, design and voltage too. Don't pair an AGM with a flooded, nor a lithium with a lead acid, nor an AGM with a gel etc. Pairing a 12 and 24 voltage battery would be .... interesting .... from a safe distance.

What about similar battery types but different amp hour ratings? Can you connect a lifepo of 100ah in parallel with a 150ah battery and use the same BMS on both?

 

[RCinFLA]

Just normal aging and usage over time will cause variance. It is not too big an issue unless you are drawing high peak currents that cannot be supplied without near full contribution by all parallel batteries.

What typically happens is one leg will initially provide more current then other legs. This will change with other legs starting to supply more as discharging continues. This is why you have to watch your peak current demands. Recharging is similar so watch your peak charging currents.
Expect a newer battery to 'show up late to the party' for current drain contribution compared to batteries that have been used. (lead-acid batteries) This will change as lead-acid batteries get into old age with higher internal resistance caused by positive plate grid corrosion so their overall AH contribution will be significantly less.

For parallel strings of higher voltage, series stacked batteries I prefer not to parallel strap sub-batteries together. This way you can put a clamp on ampmeter or hardwired shunt to each leg to monitor how much current imbalance there is.

I have run 10 parallel 48v batteries (four 12v in series x 10) strings for over 25 years successfully this way. I keep same age batteries in a series string. I usually try to replace the oldest one or two strings every year to keep up on overall array condition. (and avoid breaking my back). That cost me about $800 a year for replacements.

 

[RCinFLA]

What about similar battery types but different amp hour ratings? Can you connect a lifepo of 100ah in parallel with a 150ah battery and use the same BMS on both?

If they are from same manufacturer of same type just different AH probably be okay but I would not do if avoidable. Definitely avoid mixing in series string as you will limited by lowest AH battery in string.

Small variance in manufacturing chemical batch mix may cause some variation in average cell voltage for given state of charge. For lead-acid, just slightly different electrolyte acid concentration causes difference. Higher acid concentration in lead acid is like 'speed drug' to battery. Live fast and die young.