I've found them from Walmart for less than 20$. Run it straight to your plug. Bypass switch. They are notorious for failing. They finally corrected this issue on the new tanks with a magnetic switch. Fingers crossed.
. By the way, the Tsunami pumps are pretty bulletproof and is unlikely the issue. Test your battery with a cheap multimeter from harbor freight. You can get one for free with any purchase, if you get the coupon.