Commando Battery Draining

If you still have the blue capacitor fitted try disconnecting it (insulate any exposed terminals). It is often said they can drain the battery and many owners remove them to prevent this with no lie effects.

If you disconnect the battery when not using the bike and it is fine when reconnected this means it's an issue with bike not the battery

A cell in a lead-acid battery should yield 2.2V.

6 cells X 2.2V = 13.2V when fully charged.

It would seem that your battery is not coming fully up to the mark.

Do you have a charger that can be left on for a day or so to see if it will come to a full charge?

Previously john_cole1 wrote:

Recently fitted Alton starter, but now find that the battery goes flat after about a week. Checked battery off machine new 12v18amp shows 12.8 on multimeter. which will then keeps charge on bench. How do I check wiring to show which item is causing discharge please. 1972 Interstate, previous battery was pretty much shot so problem may have been there before fitting Alton.

Hi John,

To check what is draining the battery simply put the multimeter onto Amps and put in series with the battery (disconnect all the wires from one of the terminals and put one wire from the meter on the battery terminal and the other wire on the wires you have just disconnected). Put the meter onto the 10Amp range, Turn the ignition on, you will see 2 or 3 amps. Do NOT press the starter button !.

Now turn the ignition off, the current should drop to zero. Now switch the meter to the milli amp range (mA) it should still show zero. If not then you need to start removing wires from items to see what is causing it.

The thing to remember is that most items are the other side of the ignition switch so it should only be things like the blue thing and the voltage regulator (Zeners or power box) that can cause the problem.

Regards

Tony