72v battery bank. Lead acid.

[Sraycwb]

I came across this in last day or so.

6 12v lead acid batteries, wired up to a single anderson connection, 72v. 7.2ah?

Battery manu unknown at this point but its priced so low I thought I'd be robbing myself if I didnt.

Thoughts on this being the power station?

[john61ct]

What on earth do you think you need 72V for?

For deep cycling, the specific maker and model are critical for long term value.

That set might only last 150-200 cycles, where 6V Duracell/Deka's well over double or even triple, given equally diligent coddling.

Those are usually under $100 per unit for 200+Ah capacity.

7.2Ah capacity won't do much for a House bank.

[john61ct]

And you really need to know what you're doing buying second-hand batteries, even if tested by myself before handing over any cash, at over 95% SoH, I would still not pay over 30% the new price.

And of course would not even think about it unless knowing for sure they were a good quality mfg and model specifically designed for my use case.

[Sraycwb]

I concur with all the above. For fiddy bucks, I had to second glance it, lol.

[dzl_]

Very interesting find, I wonder what it was used for.



I sorta share John's sentiment: "Why?"



How cheap is cheap?


What is the use for 72V? (72V is well outside of the 'reasonably safe' low voltage range).


Can you easily find a 72v inverter or charger at a reasonable price?



Are you sure about the Ah specs, It seems weird that the Ah specs mirrors the voltage.



7.2Ah @ 72V is roughly 520Wh, put into perspective that's a little less energy than a 50Ah 12v battery.

[JackE]

First off, I know nothing about what is good or bad in the battery bank world, so I'm just shooting out questions to gain some knowledge.

If they are 12V, can't you just switch them to parallel rather than series and have a decent 12V bank?
Would that change the aH rate?
And for $50, it's worth taking a chance on the batteries just to get that nice storage case capable of housing 6 batteries! I paid $15 for a single battery box at Walmart for my trailer.

[sepudo]

I agree. Swap the wiring and have a good looking 600ah @12v set. Remember to use proper Guage wiring as you'll now be uping the amps

[dzl_]

Originally Posted by JackE

If they are 12V, can't you just switch them to parallel rather than series and have a decent 12V bank?
Would that change the aH rate?

Yes the stored energy will be the same either way (520 Watt-hours) but:

6 x 12v 7.2Ah batteries in series = 7.2Ah @ 72V (520 Watt-hours)

6 x 12v 7.2Ah batteries in parallel = 43Ah @ 12V (520 Watt-hours)



But based on the info OP provided, they are unknown quality, unknown manufacture, used batteries, in unknown condition, with about the same capacity as a single 12v 50Ah battery (unless I'm misunderstanding what OP meant by 72v 7.2Ah)

Originally Posted by sepudo

I agree. Swap the wiring and have a good looking 600ah @12v set. Remember to use proper Guage wiring as you'll now be uping the amps

Based on the info given, these are 7Ah batteries not 100Ah.

6 x 7Ah batteries in parallel is 43Ah @ 12v

[sepudo]

Still would test them in parallel but looking at the footprint that they occupy they actually may have been too pricey at $50 lol

[sproutroot]

Doesn't look like 7 amp wiring to me. It's very tough to tell by the picture. What I can tell is that the terminals are weird, and here's what a quick googling got me: https://www.batterystuff.com/batteri...onic-security/

Seems like those battery terminals are used for batteries that top out around 12 AH, and could be as low as 1.3 AH.

Seems like a well built system for $50, but I'm not sure what it'd be good for.

I'd guess it was an uninterrupted power supply - wilder guess it was for sound equipment.

[Native]

The batteries look to be out of a UPS (Uninterruptable Power Supply). Those are typical connectors used in them.

[john61ct]

Putting more than a couple strings (series'd cells, aka batteries) in parallel is not optimal, reducing total capacity and lowering lifespan.

3-4 would be my maximum. Really, the only reason to have any paralleling is for mission-critical redundancy if modules fail when you are far from civilization.

Two strings in parallel gives you that.

So, first you need to know how much Ah capacity you need at your selected system voltage.

Then you select your cells /battery modules accordingly.

And again, for deep cycling, you need to choose modules designed for that. UPS usage is completely different, designed to maintain capacity sitting at Full for 99.99% of their lifespan, only actually cycled very occasionally.

A House bank off grid can get fully cycled (means 50%) daily for a decade or longer, if you design the system and select your components properly.

Just spotting some random collection of batteries "hey those are cheap!" is not a great approach

unless you're just fooling around looking to play with various battery types just as a learning exercise.