House Alarm Style 9448?

I have just come back from holiday and the power supply in my house was off. My neighbour said my alarm went off for 2 hours and then stopped.
We turned the mains power back on when we arrived home thinking the alarm would work again but it’s still not working after been on all day.
Does this mean the battery is faulty ?
Anyone any idea’s please .

It’s the Style 9448+ btw

Kind regards
Simon