Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
Check your battery connections first. Make sure they are clean, with no corrosion, and on tight.
If that all looks good then move on to testing the battery at a local auto parts store. It may have enough power to light up that small load but maybe not enough to turn the engine over.
From there it's a matter of checking the circuit to ground and to the starter.