Mixing (parallel) similar batteries

[Chris R]

Hi all,

 I just aquired 6 Trojan J305P batteries and wish to add 4 of them to my existing bank of 16 Trojan T-105's wired for 24V.

My T105's have been used for two years, and the J305P's were possibly used in a floor cleaning machine before I got them.

The T105's are 220 Amp/hr and the J305P's are 315 Amp/hr all are 6 Volt.

Shall I parallel the J305P's with the T105's after topping off the J305P's ?

TIA

Chris

Up in the Colorado Rockies

[AbyssUnderground]

It would be best not to because the lower Ah batteries would become more discharged than the higher Ah batteries, and when it comes to charging, the lower Ah batteries will get charged first leaving the higher Ah batteries discharged.

[Flux]

As long as each 24v string has identical batteries then you can connect the strings in parallel. You will not be able to use the 6 batteries.

Others will tell you this is bad, I have seen far worse things done and you are not starting with virgin batteries so there is no point in being too theoretical about things. Try to arrange the leads to the parallel strings so that the current is shared in relation to battery size.

Flux

[wpowokal]

As one who has 9 strings of paralell batteries I agree with Flux, go for it.

I make all my connection equal length, but it depends on the draw/charge amps how relevent this point is or is'ent. In the end it will all ballance anyway.

allan down under

[Seaspray0]

Think of it like having two water tanks of different size but piped together so they will have the same level.  You will drain more water from the bigger tank in order to keep the same level as you draw water.  The same will happen with the batteries.  They all will provide current toward the load with the higher capacity ones providing more current.  In parallel, the voltages will always be the same on all the batteries.  I can't see any harm in a setup like this.