# How is energy consumed when charging a battery?

When I charge my battery at a constant voltage and current, the energy supplied is constant throughout the charging process. If it takes 1h to charge to 80%, the next 20% takes another 1h.

Since I supplied the same amount of electrical energy during the first and second one-hours, is a significant part of energy wasted during the second one-hour?

I understand the battery internal resistance increases by the degree of charge. Does it mean we waste a significant of the electrical energy supplied in the form of heat?

• How are you measuring "%age complete" and "constant voltage and current"? Lots of charging systems reduce the charge current towards the end. And "fuel gauge" systems are notoriously inaccurate. – pjc50 Mar 23 '18 at 13:33
• @pjc50 good point indeed. Assume we are using a plain power supply with constant voltage and current. How will be the charging behavior? – Yoria Mar 23 '18 at 13:39
• you do waste some in heat, how much is "significant" is an opinion. – dandavis Mar 24 '18 at 17:27