How long should a battery last?

[Daddio]

Two years is definitely poor, especially as there's no alarm to drain it. I expect the warranty has expired so a refund seems unlikely! However, as others have said, it does raise suspicions about a fault in the wiring or perhaps an electrical component such as the ignition system. Check with an ammeter before replacing the battery.

I took the battery out this evening and it is an MF brand (fitted 2 years ago before I bought the bike) and ran a voltmeter across the terminals and its showing 12.8v. What will an ammeter tell me? Is this a different reading to the one I've taken? Please excuse my battery reading ignorance .

[hotbulb]

I took the battery out this evening and it is an MF brand (fitted 2 years ago before I bought the bike) and ran a voltmeter across the terminals and its showing 12.8v. What will an ammeter tell me? Is this a different reading to the one I've taken? Please excuse my battery reading ignorance .

There seems to be a budget battery brand "MF", and also a type of battery known as "maintenance free"..... not sure which you have. An ammeter will measure the current flowing from the battery into the bike's circuitry, whereas the voltmeter measures the voltage across the battery terminals.
To try to locate the problem, could you take the bike for a run of 5-10 miles, disconnect the battery,and then take a voltage reading after the bike has stood for a few minutes. Take another voltage reading after it's stood for a day, and then after 2 days. If the voltage has reduced substantially during that time, then it's probable the battery is faulty. If, however, the voltage stays up while the battery is left disconnected, then it's more likely that something on the bike is draining the battery.

[Dee Duble Yuh]

If you liken electricity to water, the voltmeter is measuring how much "pressure" there is; an ammeter will measure how much is flowing, just like a domestic water meter.

If your water pipes leak then water will be flowing through your water meter even when all the taps are closed.

It could be that a component on your bike is "leaking" current. When everything is turned off there should be no current flowing. Turn your multimeter to ammeter position, disconnect one of the battery leads, and use the multimeter to bridge the gap between batter and lead. Any current then has to go through the multimeter. There shouldn't be any, but if the meter shows some current it reveals that one of your bike components is leaking current.