battery charger blinking red, not sure what it means

I am trying to charge a 36V battery for a Black & Decker battery and strimmer, and the charger is alternately blinking a slow and fast red flash. The label on the charger implies this means the temperature of the battery is too hot or too cold, but the battery has been in my house for several hours today before I started charging. Could it be a faulty battery? The charger is fine because it charged my other battery without any problem.

Try what Kleftiwallah suggested, but if it charged one battery, and not the other, under the same conditions, then I am guessing it is a bad battery. 

Some rechargeables are lithium ion, but some are the old sealed lead batteries.  The lead ones are finnicky about charging, especially if drained down and not recharged in a while, or recharged and left on charger for a long time.  I had a Black & Decker like that.

how long is it lasting on the strimmer, try it and then try recharging it.
Just in case battery is faulty, do not leave on charge without checking every so often, just in case it catches fire.