Electronics Gadget

Charging and Discharging of Batteries

The very basic principle of batteries is that they discharge to provide electrical power, and then recharge later on. In a vehicle, this is based on the fact that the battery has a 'natural voltage' of about 12.8 volts.  This means that a battery that is not being charged or discharged will tend to have about 12.8 volts between the two terminals.  This is usually referred to as the OCV, or Open-Circuit Voltage. Things get a bit more complicated when the battery is being charged or discharged; the actual voltage will be different from the OCV because it is no longer open-circuit.  At these times, the theoretical OCV is referred to as the EMF, or Electromotive Force. The difference between the EMF and the battery's actual voltage represents the amount of work it's doing (in discharge) or the amount of recharge it's accepting.

1. Batteries discharge (provide current) when the battery's EMF is higher than the electrical system's voltage, and charge (accept current) when it is less. This reaction is fundamental.  Electrical loads act like short-circuits in a way, so they try to get to zero voltage.  The hp laptop battery wants to be at 12.8, so it provides current to try to achieve a balance.  When the alternator is functioning, the system wants to be at 14.0 volts (typically) but the battery still only wants to be at 12.8, so it accepts current for the same reason.
2. While electrical loads drive the system voltage down, the charging system tries to supply enough current to keep the voltage at a certain level. If the loads win, the hp 338794-001 battery discharges to try to make up the difference. This happens when starting, when running accessories (even the clock!) with the engine off, and when the bike is running but not charging enough. If the charging system (or an external charger) wins, the load is met and slightly exceeded, so that the battery is being slightly charged.
3. Depending on the nature of your riding and the charging system of the bike, the battery may be alternately charging and discharging from time to time. This is called "load leveling", when the hp 361742-001 battery "kicks in" some power when needed, and takes it back when there's some to spare. This is OK as long as: a) more energy (at least 10% more) is returned to the battery than is removed, and b) the battery never becomes "empty". Starting is the most obvious drain on the battery, but cooling fans, electric clothing, lights and the like are all heavy system drains which might dig into the battery reserve at times (like idling at a traffic light). As long as the power is replaced in time you'll be OK, although these "deep cycles" will shorten your battery's life.
   1. Batteries should be charging during normal bike use. The hp 371785-001 battery's primary purpose is to provide current when the bike's electrical system demand is more than the charging system output, as described above. Ideally, though, this would only happen during starting; after that, the higher voltage maintained by the charging system will recharge the battery and then "float" it at a slightly-higher-than-EMF voltage. The battery would no longer be supplying power, since all demands would be met by the charging system of the bike. In reality, this does not happen on many older bikes; load-leveling (as described above) does.
   2. Although the loads may briefly overpower the charging system with no ill effect, continuous discharge during normal bike use is obviously undesirable. If this happens, the hp 372772-001 battery will probably never become fully charged unless an external charger is used when the bike is parked. However, in unusual circumstances this may be the only way to operate the bike. If the electrical load routinely exceeds the ability of the charging system, it can be ridden as long as the battery is recharged before the battery is fully discharged. Without eventual recharging the bike will not run.