My local Harbor Freight has just gotten in the Thunderbolt Solar AGM batteries 12 volt, 35 AH, for $74.99 product #68680. I started to buy one & use the 20% off coupon, but decided to wait as they have plenty in stock. Just wondering what you guys think or am I better off to spend that money on a deep cycle batt at Walmart?

My HF is just now re-laying their shelves for the "thunderbolt" series of solar stuff. They got in the 5 Watt solar panel with power pack, and had empty space for new stuff.

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I give Harbor Freight "E" for effort, but $75 for 35 amp hours is real expensive.

Optima yellow top AGM batteries go for $200 and they are 55 AH. The HF battery is a good price for an AGM. You can't really compare AGM to 6 volt golf cart batteries that are four times the weight and amp hours. AGM batts have their place. For example, I have a 12 volt refrigerator for the car. A flooded acid battery is not very safe in terms of vapors and spillage in a confined space. This is a good use of an AGM.

Good point Myles, I sorta forgot that Harbor Freight is in an "CYA" situation here selling a battery like this out of retail locations. They basically needed to be a battery that some guys kid will be dragging around the store before it even gets to the cash register.

And while they appear expensive, none of us buy any of this stuff without using a 20% off coupon. Soooo....

Point well taken, it's comparing apples and oranges.

Sam's Club sells a Duracell® AGM Golf Car Battery - Group Size GC2AGM for $159.73.  This does not include core charge and taxes.  It is only available in some states.  It is rated at 190 ah.  I bought my 4 Optima D34's from Sam's before they started selling this battery.  It might be worth looking in to for those thinking about AGM's instead of flooded cells.  It is 6-volt, so a 12v system would require them in pairs.  Just passing this along..

I'm trying to understand batteries better. Looks like the Duracell might be good?

My fridge draws 2.78 amps. My freezer draws 1.13.  So that's about 4 amps. Based on the below specs for the Duracell, does this really mean that I can power my fridge and freezer for 38+ hours of running time? (60\2304=38.4) with two of these batteries (for 12 volts)?

  • 1 amp hour rate:103
  • 100 amp hour rate:220
  • 20 amp hour rate:190
  • 3 amp hour rate:145
  • 5 amp hour rate:163
  • 6 amp hour rate:167.8
  • 8 amp hour rate:173.7
  • BCI Group Size:GC2
  • CCA at 0 degrees F:680
  • MCA at 32 degrees F:900
  • Minutes at 15 amps:718
  • Minutes at 25 amps:409
  • Minutes at 5 amps:2304
  • Minutes at 50 amps:171
  • Minutes at 75 amps:94
  • Minutes at 8 amps:1409
  • Reserve Capacity:380
  • Volts:6

I recommend you buy a Kill-A-Watt meter.  It plugs into the receptacle, then you plug the appliance into it.  It will give you a reading of the power usage over time.  That is the numbers you really need to work toward.

I have one. That's where the amp draw numbers came from. When my freezer is running, the amp part of the Kill a Watt reads 1.13, the fridge 2.78. So if the amp draw (minutes at 5 amps) is 2304 per the battery specs, I took that to mean 2304 minutes running time at a 5 amp draw. Since my amp draw for my fridge and freezer is 4 amps...


If the numbers came from the Kill-A-Watt, then it's amps @ 120 volts. 4A x 120 volts = 480 watts. It will still want 40 amps from the batteries at 12 volts to make the conversion. 40A x 12 volts = 480 watts. Plus efficiency loss for running it through an inverter.

So  how do I figure how long the batteries will last at that 4 amp draw?

The ambient temperature and the resultant time of the duty cycle on the fridge are very important variables in determining amp draw. 480 watts seems like a lot for a fridge. Are you sure it's not 48 watts?

About 500 watts when it is running is normal, but it is not running 24/7/365.They only run a few minutes per hour.

They make refrigerators that are specifically made for off-grid use and those units will use less power.

But,... to get a better picture, they should be plugged up to a kill-a-watt 24 hours to see what the real wattage consumption is per day and then calculate from that info.

Since we last visited this post we have bought one of these HF batteries and just for the's a brute! We are using it in our portable solar generator and this thing is holding up great. We just can't knock it down. Still ramps right up to the high 14's even after "finally" touching 12 volts a few times. And we are only using three panels from the old HF kit with it. This battery is "suspiciously" tough.


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