UKH

I've inherited an 80Ah battery that I've no obvious use for. It holds a charge so I may just keep it topped up in the garage for winter jump starts if needed. Any better ideas?

With 12v LED spotlights lamps (GU 5,3??) you can rig up emergency lighting for power cuts that will last an awful long time at quite good light levels.

You can choose cool "flat" light for workplace or warm for warm lighting and reading.  They only consume about 5W but give the equivalent of an awful lot more!

I use them with Clansman 24v batteries as they plug straight into the charging/output receptacle and you immediately have a spotlamp/uplight/camping/emergency light.

They run from about 10v up to at least 28v (I've tried them for long periods).

After you've used it for max hangs until Christmas, you'll be able to use it for a paperweight 😜

On November the 5th, put a heavy duty spanner between the terminals, and watch the sparks fly.

get a 12v to usb converter and use it as a car camping power bank for all the family’s devices. Use it for wild camping too if you are a bit mental 

I always keep an old car battery on trickle charge in my garage, useful for all sorts of things. It helps that I had a suitable charger lying around from motorbike days.

I've used it for jump starting and as a power supply for testing various van related kit like stereos, fixing my van fridge etc. Most original use was for a home made spot welder to repair my kettle. It worked well, I discovered you can get over 1200A out of an old car battery.

Doorstop?

Have a google on making ball lightning.  You probably want a second battery in series and some welding cable sized to limit the current to < 400 A without getting hot enough to melt its insulation.

Vigilante interrogations. Everyone thinks they're a cool customer until the gonad electrodes get taped on.

Apparently.