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Directly below is the overview of a project that has been working well for around three months.

A 6 Watt, 12V LED spotlight powered by a 12V 7Ah sealed lead acid battery, controlled by a timer switch that runs the light for 10 hours a day. The battery is charged by a 12V 50 Watt solar panel with a solar charge controller between the panel and the battery.

The problem that started occurring a little after three months is that the battery will no longer run the light for the full 10 hours. When the battery was fresh from the store, I had timed how long the battery could run the light straight, and it was close to 13 and half hours. When I was doing the math for how much battery I needed to run the light for 10 hours, I did not take into consideration that lead acid batteries do not like being fully discharged on a daily basis. I believe I have ruled out the solar charging as a suspect by charging the battery on a battery charger with the same outcome.

Is there a particular type of battery that would be better suited for this type of usage or would my best option be to get a sealed lead acid battery that can handle 10 hours while only being discharged 50/60/70 percent?

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    \$\begingroup\$ Do you have some sort of battery charger between the solar panel and the battery? If you just directly attach the solar panel to the battery, the battery will get brutally overcharged and damaged. 50W at 12V is almost 4A, overcharging it at this current will ruin the battery in almost no time. Also, what's the output current of the battery charger you tested with? Does it switch off when the battery is full? Is it one of those car battery chargers? \$\endgroup\$
    – Jonathan S.
    Oct 28, 2017 at 16:14
  • \$\begingroup\$ @Jonathan I do have a charge controller between the panel and the battery. I updated the initial question with the information as well since I had forgot to initial include it. The link to the one I am using is at the bottom of this comment. The output of the battery charger is just 1A, it was a tiny charger that came with the battery. It does switch off when the battery is full. Solar charge controller \$\endgroup\$
    – theCalmChameleon
    Oct 28, 2017 at 16:21

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This battery (Yuasa NP18-12, 12V, 18Ah) should be better suited for your needs.

If you look at the "Typical discharge characteristics NP range" graph in the datasheet (last page, bottom right), you'll see that the battery loses most of its capacity within just under 200 cycles if you discharge it completely in every cycle. This is exactly what's happened to your 7Ah battery - you ran it at almost 100% depth-of-discharge and it lost a lot of capacity in about 100 cycles.

The key to a long-lasting battery in your application is using a battery rated for cyclic discharge with way more capacity than you actually need. The NP18-12 is such a battery. In your case, it will run at 30% DOD, so it should last for more than 1000 cycles or about 3 years according to the datasheet.

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