Help phone automatically restarting when fully charged!

[Africanguy44]

Hello I have a Samsung Galaxy III mini 8gb , GT-I8190N. My problem started less than a month ago . if I would use Map My Run or Google Maps after a short time my phone would restart by itself then say my battery needs connected to a charger. It was fully charged but now can't even use these applications because I know my phone will restart and say my battery is dead but I can power off wait 10-15 minutes and power on and it says I have 70 % percent left on my battery so my first thought is a new battery. I have had this phone for 15 months so what is the life expectancy of this battery? Feel free to email me at africa35@gmail.com