A battery can be divided into three intrinsic sections consisting of the actual energy that is available to the user, the empty zone that can be refilled, and the rock content that has become unusable. Figure 1 illustrates these three sections. The three sections of a battery consist of available energy, empty zone and rock content. The loss of charge acceptance of the Li-ion batteries is mainly due to cell oxidation that occurs naturally during use and as part of aging. Reading internal resistance of a charged battery provides some clue, but its health remains guesswork.
All lights are lit when the battery is fully charged.
On a partially discharged battery, half the lights illuminate, and on an empty battery all lights remain dark. Figure 2 shows such a fuel gauge. A user unfamiliar with this battery has little information about how long the pack will run. Figure 3 shows such a tri-state fuel gauge. The SMBus, on the other hand, has been proven to perform this task well.