Spare head lump

During I returned to home by bicycle in the night, battery of head lump was wasted. So, I had to run in the dark without the light.
The battery have a alarm of lack of electricity. But, the time from the alarm appeared to turning dark was very short.
So, I bought head lump and rear lump as spare. They are cheap and not have a good performance. But, I think it is enough as spare.