NEW YORK (AP) — When a heat wave hits, millions of air conditioners switch on at once, straining the electric grid and driving up the risk of outages — and residents’ power bills. To ease that strain, power companies may ask customers to do something many probably won’t: Set the air conditioner a few degrees higher. Now, a renter-friendly pilot program in New York City is testing a different approach: plug-in batteries that can power air conditioners offline during peak demand, helping take