Battery mixing/matching question

[noxin]

I've read plenty about the importance of trying to keep all your batteries the same date, brand, etc for the purpose of getting the maximum life out of them, but I'd like some feedback on this situation....

I have a set of Trojan T-105s that are dated May 2017 that I bought new last year. They are probably not used even once every 3 weeks, and when they are it's usually no longer than 20-30 minutes in my hilly neighborhood. Since the cart is used so sparingly, and the current charger is an old Powerwise (it's a 2000 Ezgo TXT), I unplug/plug it in every 4 or 5 days when it's sitting idle.

This set of batteries charges/performs like brand new, but I've upgraded to the Alltrax SR48500, HD Solenoid, HD F&R, etc. and recently got a 48v charger so I'm ready to add 2 more 6v batteries in the bagwell. Where I am, battery sellers want my first born for Trojans (especially with no core to trade), so I'm wondering if it's OK to mix a different battery/brand into the existing pack. If so, which specs do I need to look at to try and closely match what I have already?

[noxin]

OK, just read in another thread where Bob suggests not mixing battery brands, but I've also seen some respected members say it's OK in the threads I've found while searching.

[Lochlin]

Though I am not a battery expert I do know that different batteries have different charging cycle needs. For example, most new school chargers have to be configured for the brand / type of battery that is being charged. If you mix batteries then, invariably, one of those battery types won't be charged to its specifications. Now, will that make a huge difference that you need to consider? Maybe not but this is at least the logic.

[JohnnieB]

The batteries are connected in a series chain, so they are charged and discharged in series and both the charger you have and the controller only sees the average of of the individual batteries in the battery pack. When the individual batteries are closely matched, this arrangement works reasonably well, but if they aren't closely matched, the weaker batteries are over discharged when cart is used and the stronger ones are undercharged when the charger is used. The net results is newer, stronger batteries age faster than normal and quickly acquire similar aging characteristics as the older, weaker batteries, whose aging has been accelerated by the over-discharging and the entire set of batteries will need replacing sooner rather than otherwise.

Ideally, get the existing batteries load tested to determine their run-time in minutes at a 75A discharge rate, then find some used same brand batteries with as close to the same run-time at 75A as possible.

Also, a new battery that is the next step down might have about the same run-time as the existing ones.

Whatever you do, replace all the batteries as a set the next time they are replaced.

[noxin]

Originally Posted by JohnnieB

Ideally, get the existing batteries load tested to determine their run-time in minutes at a 75A discharge rate, then find some used same brand batteries with as close to the same run-time at 75A as possible.

Also, a new battery that is the next step down might have about the same run-time as the existing ones.

Whatever you do, replace all the batteries as a set the next time they are replaced.

Thanks guys. I plan on changing over to six 8v batteries whenever it's time to replace them, but since these batteries have so little run time on them I consider them pretty new. I doubt they've ever been below 95% SOC, though I'm sure the constant top-off charging has still aged them.

I'm not really concerned about the 2 new batteries aging prematurely because of the condition of the 6 existing batteries, rather would 2 new ones negatively affect the existing ones? And would it be acceptable to add a different brand battery to Trojan T-105s without having any load test results?

For info, charger is a Schauer JAC1548H