Solar battery charger

Howdy, I’ve got Gallagher Electric Fence monitors that run on 6 x AA batteries. While the batteries last around 12 months, it’s a pain having to replace them all. I’m thinking about putting a rechargeable battery on it with a solar panel to maintain the power.
I’d like a bit of a hand selecting a panel, regulator and battery from someone who knows!
The 6 x AAs are in series giving a 9V supply. At 2000mAh/battery, I’m assuming that gives a capacity of 12Ah. That lasts around 12 months, so I’m thinking a rechargeable 9V battery (eg these ones on Amazon) might be enough with a solar panel attached. I’m not sure how to size the solar panel for the battery though.
Any help would be great.


I am in the prototype phase of building a solar power supply to power WYZE cameras that are located around my property. This is a 5V @1A system with approx. 13Ah of capacity. Uses 4x 2.5W @ 5v panels, 18650 (3.7V) batteries, parallel TP4056 controllers, and a buck converter.

This design will not meet your needs but may provide you with some context for what you will need for a complete system.

Solar-Camera-Power-Supply.pdf (84.6 KB)

In my experience, solar power design is a complex interactive process of choosing compatible systems components in the context of the operating environment. It’s not as simple as I thought when I started and I’m not sure that I have gotten it right yet.

Design considerations:

  • Overriding cost goal
  • Solar panel technology: size, voltage, capacity, array, wiring
  • Battery technology: voltage, capacity, chemistry, wiring, packaging
  • Controller: charging method, voltage, current, packaging, wiring
  • Packaging technology: long-term protection from the sun and environment for all components. This is tougher than I thought. I live in Utah which has hot dry summers and rain, snow, and ice in the winter down to 10 degrees F. Water, expansion/contraction, sun damage etc. make this packaging tough.
  • Based on specific geography how many panels and in what position will you need to attain enough power across weather conditions?
  • What will your controller do when there is no sun? I found out that some controllers will shut down and drain the batteries :(.

**Warning: The below is a “back of the napkin” guess to help you get started.
There are many choices for components on Amazon, these are just a few. A more detailed selection process where each component is researched for fit/function would be advisable.
Use readily available panel-controller configurations and convert the output to 9V.
Assuming your average current may be pretty low <1amp and capacity are 2Ah these are example guesses at components, I have not done the complete math workup…
Solar Panel:
Did not find any 9V panels, 10W-12V panels, good packaging:
Charge Controller:
12V charge controller, <$$, ready to use packaging, Reviews were marginal:
12V charge controller, few reviews, require packaging:
Since 9V batteries are only 280maH, lots of batteries and their connections are problematic. Instead, use one 12V Li battery:
15 Ah:
Buck Converter:
12V to 9V step down:
Other considerations:
Connection of this solar system’s output to the fence monitor
Overall packaging and mounting
Remote monitoring


6 1.5V @ 2000mAh in series is 9V @ 2000mAh when in series since the current flows through each battery. If they were in parallel then the capacity rating would increase. It will take you 8 of those 9V 280mAh batteries in parallel to get you 9V @ 2000mAh and NiMh at 9V is not a normal setup but you might find a charger for that.

I would look for a 12V solution since 12V chargers are a dime a dozen and a buck-converter at 2A or better are cheap. Like this for example:

Also, 9.6V is pretty common for RC systems so that might be an option for pre-made packs and chargers too.

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Great, thank you very much for your comments.

Super, thanks very much.