Bike been sitting few days at the time since it's always raining. Still, should i have put a tender on it? Can a tender recharge it in a night?

What can cause this? Battery is 20 days old...

 

I would double check ALL the battery connections AT BOTH ENDS OF EACH CABLE! Make sure that all the connections are clean AND tight. A tender won't really charge up a dead battery in as much as maintain a charged battery. Put a real charger on the battery and once the charge tapers off take a volt reading with a load tester. A fully charged battery should read 12.9 volts! A 12.7 volt reading means that the battery is 25% discharged! Under a load the battery should hold it's charge, NOT drop off below 12 volts!

Beyond that, when running the bike the battery should read 14.2 to 14.3 volts. That means that the regulator is working!

Remember that all the connections need to be clean and tight!

 

This is a long shot however I have heard that some batteries sit on a dealers shelf for a long time. Shelf life on a Harley battery is only a couple of years.

 

My old lead acid batteries used to sit for almost a month (no tender), and usually started right up. Any longer and I had to pull it and charge it. 20 days seems very unusual to me. Most my lead/acid batteries lasted about 6 years, even without ever using a tender.

Instead of finally maybe buying a tender and another lead/acid or AGM, I bought a Shorai Lithium battery. Dropped 10 pounds of weight, and instant powerful starts, even after almost 2 months! Instant starting, boom!

Life is good with a Shorai. They are a bit more pricey, but not much if you figure buying a tender for the AGM too. The peace of mind over my old lead/acid units is another bonus I never realized until purchase and some time with the Shorai. I know when I hit the start button it's gonna start.

John

 

i had a 2012 Sportster 1200 custom, my problem which ended up being a recall was the voltage regulator. hope this helps.

 

You didn't tell us anything about the bike like YEAR & miles, but if your bike has a security system it can/will kill the battery in 20 days.