Boulevard C90 Having trouble w/keeping battery charged.

To determine that, you will need a voltmeter and a battery charger. first, put battery on level surface and check to see if the acid is at a good level, if not, you will have to get some at a parts store and refill it to level indicated on the side. fully charge the battery over night with the charger taking the battery out first. the next day, disconnect charger and write down voltage obtained from voltmeter. next, install battery on motorcycle and try to start it. if it's starts, use voltmeter to check voltage at battery while running engine, write it down. let it run a few minutes like 20 and shut it off. check voltage, if it droped, your alternator is not charging. if it's the same as when you first tested it at 12 volts, you might be good only if you had to refill it, if not, the battery is defective and must be replaced.

Check your battery first, if it's more than 2 years old, it could be had it. Disconnect the battery, and check the voltage with a multimeter, if the reading from your battery alone, is less than 12V, then your battery is no good.
To check your alternator function, using your existing battery, start the bike up, and check the voltage reading at idle, should be about 13 - 14Volts if your alternator is charging the battery.

My suzuki boulevard c90t has a cobra power commander fitted and i am going to service the engine.as i am going to order filters and i do not have a manual,is it likely that there is an after-market high flow k&n filter fitted to compliment the power commander.the bike is not kept near me so i cant check.