Solar AGM Battery Bank


They were kept properly charged, kept indoors, temperature monitored, they have all failed.  Their State Of Charge (SOC) was never below 80%, most times around 90% at night, and returned to 96%-100% SOC each day.  NPP used to have a 2 year warranty on these batteries, but have since reduced it to only 1 year.  That should be a clear warning.  Evidently, they know there's an issue.

I contacted the seller, NPP International Inc. via Amazon, where I purchased them.  They simply said the warranty is now a year.  No explanation, no offer to do anything, no pro-rating them, and not even curious to the testing that was done or the conditions they were used. 

I will gladly praise any company or product that I've had good success with, even though I don't get freebies or endorsements.  That said, when they burn me, I'll be upfront and honest about that experience too.

I spent about $1825 on these batteries.  I will be taking them as a core exchange, and buying much less expensive lead acid golf cart batteries once again.  My previous sets have lasted me 5-6 years in the past.

I will be making a video showing how these batteries have been used, how they are monitored constantly, the testing that was used to determine that they are now dead, and ultimately, the transistion back to wet lead acid batteries.


I've been using wet cell lead acid batteries over the many years of my ever growing solar setup.  They are relatively inexpensive, somewhat forgiving, and work quite well.  The downside is they do off-gas, which is why I put them in an outdoor ventilated enclosure.  They require watering every month here in sunny Florida.  And because they off-gas, the terminals occasionally need to be cleaned.

AGM batteries are initially much more expensive.  But they can last twice as long, require no watering, no maintenance, no corrosion issues, and can live safely indoors.  They also have a much lower internal resistance.  This means much less energy is wasted in the form of heat when recharging the battery bank, making my solar panels much more effective.  It also means they can supply an incredible amount of current.  Per the manufacturer's specs, each of these batteries can supply up to 1400A for 5 seconds.  This should prevent sudden low voltage spikes when an inverter gets a heavy load.  It also emphasizes the need to have a fuse on each battery.

I ordered these from Amazon.  I was considering another brand, but the vendor only wanted to sell up to 3 per customer.  These were about $30 more, but I could get all 5 at the same time.  Free shipping!  Important factor when pricing.  These weigh 138 lbs. each.

My concept drawing:

These dimensions were used for the build.

I 3D printed the stop plate, with holes for the 1/4-20 stainless hardware.  This made drilling the holes in the steel quick and accurate.

The frame was constructed from 1"x1"x0.12" steel tubing. 

I used a small TIG welder to stick the parts together.

The steel tubing is welded on all edges, the aluminum battery stop plates were bolted on, a set of heavy duty casters were installed, and a fresh coat of paint.

The plywood was harvested from the lower shelf of the workbench I modified.

The workbench is a 2x4Basics kit.  The lower shelf had a 2x4 box frame connecting the 4 legs together, with a piece of plywood on top.  I removed the plywood, and cut the back 2x4 out of the frame. 

I had to go back and remove the few inches more to make clearance for the battery cart.

Now the battery cart rolls under the workbench, which also has wheels.

Plenty of clearance between the battery cart, and the workbench shelf above it.

They finally arrived.  I had the delivery guy set the pallet directly underneath the Harbor Freight attic hoist I have in the garage.

I bought 5 of these.  They will be individually connected to copper bus bars to maximize their performance.  All totaled, my battery bank will be 12V @ 1000 AH.

Rather than risk injury, I let the attic hoist do all the heavy lifting.

Same deal, just viewed from the other side.  Now you can see the battery cart in the background.  I just swung the battery into position onto the cart.

With all the batteries loaded, the cart is over 700 lbs.  The frame and wheels handle the weight easily, but moving it was a challenge.  Once it was rolling, it was fine.  Turning it was another story.  I used a 2x4 under the edge of the cart to leverage it the direction it needed to go.  Each caster has a brake, but rolling away isn't a factor.  The hole above the batteries is where all the cables will be routed.

Now the workbench rolled into position.  I will add a Lexan door in front of the batteries to keep anything from shorting out the terminals.  This will still allow for visual inspections, and quick access for periodic cleaning.


I'm using the same 2 gauge welding cable with 175A Anderson quick disconnects.  My old setup only used 4 pairs.  I needed a 5th, so I had to order more cable from WesBell Electronics.

Here's the specification sheet on these batteries: LINK

Blue Sea makes a battery mounted fuse holder.  By installing it directly to the battery, all the wiring is protected.

The fuse is a cube shaped widget.  They are available in different ratings.  I'm using 175A fuses. 





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Last updated 11/05/19    All rights reserved.