Different battery chemistries have different memory effects Image adapted from: Chris Campbell; CC BY-NC 2.0

Some batteries never forget

The memory effect of rechargeable batteries

Have you noticed your rechargeable batteries don't seem to last as long as they did when they were new? This memory effect occurs in some rechargeable batteries when you don't sufficiently discharge them before recharging. The batteries then ‘remember’ where they were up to in earlier discharge cycles and won’t recharge fully.

Cordless drills
Many cordless drill users will be familiar with the dreaded memory effect of Ni-Cad batteries. Image sourced from: digital internet; CC BY-ND 2.0

In some battery cells, the memory effect is caused by how the metal and electrolyte react to form a salt (and the way that salt then dissolves again and metal is replaced on the electrodes when you recharge it). In our ideal battery cell, we would want a uniform coating of small crystals of salt on a perfect metal surface, but that’s not what we get in the real world. Crystal formation is very complex, as is the way metals deposit during recharge. These imperfections mainly depend on the charge state of the battery to start with, the temperature, charge voltage and charging current. Over time, the imperfections in one charge cycle can cause the same in the next charge cycle, and so on, and our battery picks up some bad memories.

The memory effect is strong for some types of cells, such as nickel-based batteries. Other types, like lithium-ion, don’t suffer from this problem.

This article was adapted from Academy website content reviewed by the following experts: Dr Anand Bhatt Research Team Leader, Advanced Energy Storage Technologies, CSIRO; Professor Maria Forsyth FAA Chair, Electromaterials and Corrosion Sciences, Deakin University; Professor Ray Withers FAA Research School of Chemistry, the Australian National University; Professor Guoxiu Wang Director, Centre for Clean Energy Technology, University of Technology Sydney