When I bought my Halo Bolt Emergency Charger it said once the Halo Bolt was fully charged it will stay charged for up to 6 months.
That has proven to be true as I haven't had to use the Halo Bolt yet in 6 months and then when I did need to use it the Halo Bolt worked great after sitting unused for 6 months.
It's best to check the charge often though and plug it in to keep the battery fully charged up so that it will be ready to go when you need it.
Just plug the Halo Bolt in and it should tell you if it is charged or not and needs more charge.
The Halo Bolt is a wonderful battery backup and Jump Starter and I highly recommend it to anyone who has a vehicle or just needs a battery backup.
It really does work great like they say it does on TV.