Thoughts on used AGM batteries?

PNW_Steve

Hello Everyone,

I am struggling to get the most bang for my $$ as I can in my solar system. Batteries have been a big hang up.

I have drooled over AGM's then turned my attention back to Sam's club GC2's. Then yesterday I came across a retired gentleman when has just moved back into town from his off grid home in the mountains. He is selling off his solar system.

He has 4x L16 AGM's offered for $500. They are two years old and he insists that they were cycled to no more than 20% DOD.

Good deal or run away?? Questions to ask the seller?

Thanks.

westbranch

What brand? that is important...$125 each? I presume they are 6 Volt units..... If so I would bite the hook... 2 years is a reasonable break-in  and should give you OK service.
Ask about the rest of his system... other components for sale?

softdown

Still $500 for what could be almost ideal or close to trashed. I'd recommend a SG test though showing resting voltage of 12.7 at  ~70F is a pretty good sign....after the batteries have sat for a day.

 If he isn't solar savvy enough to charge up batteries for sale, I might be concerned. 

mcgivor

softdown said:

Still $500 for what could be almost ideal or close to trashed. I'd recommend a SG test though showing resting voltage of 12.7 at  ~70F is a pretty good sign....after the batteries have sat for a day.

 If he isn't solar savvy enough to charge up batteries for sale, I might be concerned. 

The problem is doing  a SG test on AGM, it's not possible, open circuit voltage or load testing are about the only way to determine condition. Open circuit voltage can be very misleading, capacity could be close to zero but voltage appears good, removing surface charge will give more accurate results. 

Ocean

Load Test:  Bring your inverter, voltage tester, and a small motor like a drill or a skill saw that the inverter can power.  Also a cable to connect two or four of the batteries in series. If your inverter is 12 volts, make two sets of two batteries (each set series for 12v).  Or, if your inverter is 24 volt, connect them all up in series.  Run your saw for 5 seconds, and while it's running, check the voltage of each battery.  Do it once for each battery.  The voltage should drop down a bit, then hold while powering the saw.  If the voltage drop is consistent, and not too low, you know they are fairly good.

Anyone here have a good idea of the expected voltage drop from a 1000 watt drill, or 1500 watt draw like a skillsaw?

fairly rough test but I think it would give you an idea.  Even if the batteries aren't full when you check them, it would show if they are consistent...

PNW_Steve

Thanks for all of the suggestions.

I am seriously riding the fence. The batteries are a 4.5 hour drive from me.

Hmmmm...

Estragon

Gotta wonder why he didn't sell the batteries with the off-grid cabin. Maybe the buyer knew enough to load test them?

softdown

FWIW. ...playing with batteries is a hobby of mine for a few reasons. Naysayers will yell but voltage is a dang good clue about battery capacity at least 95% of the time. 

westbranch

this question may be the clue... Is he selling the rest of the system with the cabin? if Yes, then as Estragon says.. Gotta wonder why he didn't sell the batteries with the off-grid cabin.

Marc Kurth

Battery brand, date code, standing voltage and voltage while running under a known load for 30 minutes would tell me enough to take the deal or walk away.

I often come across strong used batteries and I "rent" them to customers like this:
Say the scrap value of an L16 is $50.
I sell it for $15 with the agreement that he will bring it back to me when it dies so I can get my scrap value out of it.
In essence, the customer "rents" it for a few years for very little money. I still get my scrap value out of it, I just have to wait a bit.

This has helped a lot of people get up and running.

Marc

PNW_Steve

I contemplated the question a bit too long and someone else bought them.

thank you all for the input.