This ESR 10000mAh MagSafe battery pack is currently on sale for $12 as an Amazon Lightning deal

Honestly, this deal should need no explanation. It's a 10000mAh MagSafe battery pack, which is double the capacity of the standard battery, it's made by ESR, which is a fairly well-known brand, and it's only $12. We rarely see these things drop below $20, let alone $15, so take advantage of it while you can. It's an Amazon Lightning deal, meaning it will expire either when inventory runs out or at the end of the day.