Your next group birthday gifts should be home batteries. Most birthday gifts are forgotten within a year. Batteries save your friends money every day and keep essential devices running when the power goes out. A 5 kWh battery costs about €1,600. That is expensive for one person and easy for a group: eight people contribute €200 each; sixteen people contribute €100 each; thirty-two people contribute €50 each. Create a battery birthday club. Buy each friend a battery on their birthday until everyone has one.