Vrla charge

my friend gave me battery, where is written: valve regulated lead acid battery, constant voltage charge 15v. i want to charge it directly from dc adapter, which gives 15v dc. the problem is that the battery has 3 wires, black, blue and red and anyone please tell me, which wire is gnd, which vpp, what is the third one for and where to connect? thanks in advance

You did not say what battery!\
The extra wire is probably for the temperature sensor. (blue)
You can guess what red and black are for.