Hi All. First time purchasing a back up battery for my flashers and camera. Will also use as my battery for lights at night in the shack. Assuming that $40 at the big box stores is way overpriced which batteries have you found are cheap and work just as good? Finding a few different ones online in the $18-$20 range. Don't want junk but yet not going to pay double just cause it says Vexilar on the side.