I have a betta fish in a 10 gallon. I live in Michigan and it gets really cold here. This winter several cities surrounding us had a week-long power outage. I'm very lucky that this didn't affect my city. I want to be prepared though in case it happens in later years. Are there any good battery-powered heaters for 10 gallon tanks? If not, how can I keep my betta warm if something like this happens again?