I have a 3 AA battery powered LED camping light/lantern. It draws (measured with a multimeter in series) about 18 mA when ON and 0 mA when OFF (ON/OFF controlled by a switch button).

It’s ON all night for about 8 hours, so the batteries last only a few days.

If I use rechargable AA batteries the charge lasts less time, and with the charger I have they take a long time to charge.

My idea was to use a little SAI 7 Ah 12v AGM lead acid battery (a Salicru UBT 7 Ah), so I can power the lantern many more days with a single recharge, until the battery is 30%-50% discharged.

The battery will be recharged apart in a well vented locarion.

To convert the 12v to 4.5v I plan to use a DC/DC regulable step down converter.

I cannot use an AC power adapter.

My questions are:

1. This will be used in a bedroom, and be ON all night. Is it safe to use an AGM battery? It will only be discharged in the bedroom, not charged.
2. I plan to use a car 1 A fuse, so in case the lantern shorts, the thing doesn’t get fire. Is this a good size? Since the lantern only draws a few mA, would it be better a smaller fuse? Are there affordable smaller fuses for this kind of scenario?
3. What do you think about my solution? I am sure you can propose far better ideas that I would want to know about :)

Edit: the lantern is used (discharged) indoors, and charged outdoors.

Edit: turns out I messured incorrectly the draw. It draws 18mA when the batteries are partially depleted (3v total the 3 AA in series). But this is interesting, because at 3v the light is enough, so I could tune the DC/DC converter to 3v in order to save battery life. Or simply use the pot on the converter to set brightness up to a max of 4.5v.